Distance measuring device and distance measuring method

ABSTRACT

A distance measuring device includes a calculating section that calculates, based on phase information acquired by a first device and a second device, at least one of which is movable, a distance between the first device and the second device. The first device includes a first transceiver that transmits three or more first carrier signals and receives three or more second carrier signals using an output of a first reference signal source. The second device includes a second transceiver that transmits the three or more second carrier signals and receives the three or more first carrier signals using an output of a second reference signal source. The calculating section calculates the distance based on a phase detection result obtained by reception of the first and second carrier signals and corrects the calculated distance based on information concerning an amplitude ratio of the first carrier signals received by the second transceiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/883,269filed May 26, 2020, which is a continuation of application Ser. No.15/706,091 filed Sep. 15, 2017 and is based upon and claims the benefitof priority from the prior Japanese Patent Applications No. 2017-053380,filed on Mar. 17, 2017 and No. 2017-138307, filed on Jul. 14, 2017; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments of the present invention relate to a distance measuringdevice and a distance measuring method.

BACKGROUND

In recent years, keyless entry for facilitating unlocking and locking ofa car has been adopted in many cars. This technique performs unlockingand locking of a door using communication between a key of an automobileand the automobile. Further, in recent years, a smart entry system thatmakes it possible to perform, with a smart key, unlocking and locking ofa door lock and start an engine without touching a key has been alsoadopted.

However, a lot of incidents occur in which an attacker intrudes intocommunication between a key and an automobile and steals the automobile.As measures against the attack (so-called relay attack), a measure formeasuring the distance between the key and the automobile and, whendetermining that the distance is equal to or larger than a predetermineddistance, it is being reviewed to prevent control of the automobile bycommunication.

As a distance measuring technique, many techniques exist, such as atwo-cycle CW (continuous wave) scheme, an FM (frequency modulated) CWscheme, a Doppler scheme, and a phase detection scheme. In general, indistance measurement, a distance from a measuring device to a targetobject is calculated by providing a transmitter and a receiver in thesame housing of the measuring device, hitting a radio wave emitted fromthe transmitter against the target object, and detecting a reflectedwave of the radio wave with the receiver.

However, when it is taking into account a relatively small reflectioncoefficient of the target object, limitation on output power due to theRadio Law, and the like, in the distance measuring technique formeasuring a distance using the reflected wave, a measurable distance isrelatively small and is insufficient for use in the measures against therelay attack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a distance measuring system in which adistance measuring device according to a first embodiment of the presentinvention is adopted;

FIG. 2A is an explanatory diagram for explaining the principle ofdistance measurement by a phase detection scheme for detecting a phaseof a reflected wave and problems of the distance measurement;

FIG. 2B is an explanatory diagram for explaining the principle of theprinciple of distance measurement by a phase detection scheme fordetecting a phase of a reflected wave and the problems of the distancemeasurement;

FIG. 3A is an explanatory diagram for explaining problems of thedistance measurement by the phase detection scheme;

FIG. 3B is an explanatory diagram for explaining the problems of thedistance measurement by the phase detection scheme;

FIG. 4 is a circuit diagram showing an example of specificconfigurations of a transmitting section 14 and a receiving section 15shown in FIG. 1;

FIG. 5 is a circuit diagram showing an example of specific configurationof a transmitting section 24 and a receiving section 25 shown in FIG. 1;

FIG. 6 is a flowchart for explaining distance measurement in which twowaves are used;

FIG. 7 is an explanatory diagram for explaining a method of calculatinga distance using a system of residue;

FIG. 8 is an explanatory diagram for explaining the method ofcalculating a distance using the system of residue;

FIG. 9 is an explanatory diagram showing an example in which a distanceis plotted on the horizontal axis and a phase is plotted on the verticalaxis and the third transmission wave having a different angularfrequency are transmitted;

FIG. 10 is an explanatory diagram for explaining a method of selecting acorrect distance through amplitude observation of a detected signal;

FIG. 11A is a flowchart for explaining the time-series transmission andreception;

FIG. 11B is an explanatory diagram for explaining the time-seriestransmission and reception;

FIG. 11C is an explanatory diagram for explaining the time-seriestransmission and reception;

FIG. 12A is an explanatory diagram for explaining the time-seriestransmission and reception;

FIG. 12B is an explanatory diagram for explaining the time-seriestransmission and reception;

FIG. 13 is an explanatory diagram for explaining the time-seriestransmission and reception;

FIG. 14 is an explanatory diagram for explaining the time-seriestransmission and reception;

FIG. 15 is an explanatory diagram for explaining the time-seriestransmission and reception;

FIG. 16 is a diagram for explaining problems due to a multipathenvironment in distance measurement;

FIG. 17 is a graph showing a relation between a delay time τ₁ and adifference ϕ_(L)−ϕ_(H) of a phase change with time plotted on thehorizontal axis and amplitude plotted on the vertical axis;

FIG. 18 is a graph showing a relation between Equations (80) and (81)and Δsum32 ΔA_(H0)+ΔA_(L0) and τ₁;

FIG. 19 is a graph for explaining τ₁ dependency of ϕ_(L)−ϕ_(H) and τ₁dependency of Δsum/4=(ΔA_(H0)+ΔA₀)/4 using the same display as FIGS. 17and 18;

FIG. 20 is a graph showing a distance error ΔR without correction and adistance error ΔR with correction;

FIG. 21 is a flowchart for explaining an operation in the firstembodiment;

FIG. 22 is an explanatory diagram showing a second embodiment of thepresent invention;

FIG. 23 is an explanatory diagram showing the second embodiment of thepresent invention;

FIG. 24 is an explanatory diagram showing one of various sequences;

FIG. 25 is an explanatory diagram showing one of the various sequences;

FIG. 26 is an explanatory diagram showing one of the various sequences;

FIG. 27 is an explanatory diagram showing one of the various sequences;

FIG. 28 is an explanatory diagram showing one of the various sequences;

FIG. 29 is an explanatory diagram showing one of the various sequences;

FIG. 30 is an explanatory diagram showing one of the various sequences;

FIG. 31 is an explanatory diagram showing one of the various sequences;

FIG. 32 is an explanatory diagram showing one of the various sequences;

FIG. 33 is an explanatory diagram showing one of the various sequences;

FIG. 34 is an explanatory diagram showing one of the various sequences;

FIG. 35 is an explanatory diagram showing one of the various sequences;

FIG. 36 is a flowchart for explaining an operation in a modification inwhich a multipath is taken into account;

FIG. 37 is an explanatory diagram showing a relation between atransmission sequence and a period in which an initial phase ismaintained;

FIG. 38 is an explanatory diagram showing a carrier frequency used fordistance measurement;

FIG. 39 is a flowchart for explaining a modification;

FIG. 40A is an explanatory diagram showing, in a simplified manner, anexample of the configurations of an oscillator 13, the transmittingsection 14, and the receiving section 15 of a device 1;

FIG. 40B is an explanatory diagram showing, in a simplified manner, anexample of the configurations of an oscillator 23, the transmittingsection 24, and the receiving section 25 of a device 2;

FIG. 41A is an explanatory diagram showing, in a simplified manner, anexample of the configurations of the oscillator 13, the transmittingsection 14, and the receiving section 15 of the device 1;

FIG. 41B is an explanatory diagram showing, in a simplified manner, anexample of the configurations of the oscillator 23, the transmittingsection 24, and the receiving section 25 of the device 2;

FIG. 42 is a circuit diagram more specifically showing an example of acircuit that generates signals given to multipliers TM11 and TM12 inFIG. 4;

FIG. 43 is a circuit diagram more specifically showing an example of acircuit that generates signals given to multipliers TM21 and TM22 inFIG. 5;

FIG. 44 is a circuit diagram showing an example of specificconfigurations of the transmitting section 14 and the receiving section15 shown in FIG. 1;

FIG. 45 is a circuit diagram showing an example of specificconfigurations of the transmitting section 24 and the receiving section25 shown in FIG. 1;

FIG. 46 is a circuit diagram showing an example of the specificconfigurations of the transmitting section 14 and the receiving section15 shown in FIG. 1;

FIG. 47 is a circuit diagram showing an example of the specificconfigurations of the transmitting section 24 and the receiving section25 shown in FIG. 1;

FIG. 48 is a flowchart for explaining an example corresponding to FIG.11A in which a second device transmits phase information to a firstdevice; and

FIG. 49 is a flowchart for explaining an example corresponding to FIG.39.

DETAILED DESCRIPTION

A distance measuring device according to an embodiment is a distancemeasuring device that calculates a distance on a basis of carrier phasedetection, the distance measuring device including a calculating sectionconfigured to calculate, on a basis of phase information acquired by afirst device and a second device, at least one of which is movable, adistance between the first device and the second device. The firstdevice includes: a first reference signal source; and a firsttransceiver configured to transmit three or more first carrier signalsand receive three or more second carrier signals using an output of thefirst reference signal source. The second device includes: a secondreference signal source configured to operate independently from thefirst reference signal source; and a second transceiver configured totransmit the three or more second carrier signals and receive the threeor more first carrier signals using an output of the second referencesignal source. The calculating section calculates the distance on abasis of a phase detection result obtained by reception of the first andsecond carrier signals and corrects the calculated distance on a basisof information concerning an amplitude ratio of the first carriersignals received by the second transceiver or information concerning anamplitude ratio of the second carrier signals received by the firsttransceiver.

Embodiments of the present invention are explained below in detail withreference to the drawings.

First Embodiment

FIG. 1 is a block diagram showing a distance measuring system in which adistance measuring device according to a first embodiment of the presentinvention is adopted.

In the present embodiment, an example is explained in which a phasedetection scheme for detecting a phase of an unmodulated carrier isadopted and communication-type distance measurement for calculating adistance between respective devices through communication between therespective devices is adopted. In a general phase detection scheme fordetecting a phase of a reflected wave, a measurable distance isrelatively short as explained above. Therefore, in the presentembodiment, the communication-type distance measurement for performingcommunication between devices is adopted. However, since respectivetransmitters of the respective devices independently operate from eachother, initial phases of transmitted radio waves from the respectivetransmitters are different from each other. An accurate distance cannotbe calculated by the phase detection scheme in the past for calculatinga distance according to a phase difference. Therefore, in the presentembodiment, as explained below, phase information calculated byreception of one device is transmitted to the other device to make itpossible to calculate an accurate distance in the other device.

First, the principle of distance measurement by the phase detectingscheme for detecting a phase of a reflected wave and problems of thedistance measurement are explained with reference to the explanatorydiagrams of FIGS. 2A and 2B.

(Phase Detection Scheme)

In the phase detection scheme, for distance measurement, signals havingtwo frequencies deviating from a center angular frequency ω_(C1) by anangular frequency are transmitted. In a distance measuring device thatmeasures a distance using a reflected wave, a transmitter and a receiverare provided in the same housing. A transmission signal (a radio wave)emitted from the transmitter is reflected on a target object and areflected wave of the radio wave is received by the receiver.

FIGS. 2A and 2B show this state. A radio wave emitted from a transmitterT is reflected by a wall W and received by a receiver S.

As shown in FIG. 2A, an angular frequency of a radio wave emitted fromthe transmitter is represented as ω_(C1)+ω_(B1) and an initial phase isrepresented as θ_(1H). In this case, a transmission signal (atransmission wave) tx1(t) emitted from the transmitter is represented bythe following Equation (1):

tx1(t)=cos{(ω_(C1)+ω_(B1))t+θ _(1H })  (1)

The transmission signal reaches a target object (a wall W) apart fromthe transmitter by a distance R with a delay time τ₁ and is reflectedand received by the receiver. Since the speed of the radio wave is equalto the speed of light c(=3×10⁸ m/s, τ₁=(R/c) (seconds). The signalreceived by the receiver delays by 2τ₁ with respect to the emittedsignal. Therefore, a received signal (a received wave) rx1(t) of thereceiver is represented by the following Equations (2) and (3):

rx1(t)=cos{(ω_(C1)+ω_(B1))t+θ_(1H)−θ_(2×Hτ1)}  (2)

θ_(2×Hτ1)=(ω_(C1)+ω_(B1))2_(τ1)   (3)

That is, the transmission signal is received by the receiver with aphase shift of a multiplication result (θ_(2×Hτ1)) of the delay time andthe transmission angular frequency.

Similarly, as shown in FIG. 2B, the transmission signal tx1(t) and thereceived signal rx1(t) in the case in which an angular frequencyω_(C1)−ω_(B1) is used are represented by the following Equations (4) to(6) with an initial phase set to θ_(1L):

tx1(t)=cos{(ω_(C1)−ω_(B1))t+θ_(1L)}  (4)

rx1(t)=cos{(ω_(C1)−ω_(B1))t+θ_(1L)−θ_(2×Lτ1)}  (5)

θ_(2×Lτ1)=(ω_(C1)−ω_(B1))2_(τ1)   (6)

When a phase shift amount that occurs until the transmission signalhaving the angular frequency ω_(C1)+ω_(B1) is received is represented asθ_(H1)(t) and a phase shift amount that occurs until the transmissionsignal having the angular frequency ω_(C1)−ω_(B1) is received isrepresented as θ_(L1)(t), a difference between phase shifts of the tworeceived waves is represented by the following Equation (7) obtained bysubtracting Equation (6) from Equation (3):

θ_(H1)(t)−θ_(L1)(t)=(θ_(2×Hτ1)−θ_(2×Lτ1))=2ω_(B1)×2τ₁   (7)

where τ₁=R/c. Since the differential frequency ω_(B1) is known, if thedifference between the phase shift amounts of the two received waves ismeasured, the distance R can be calculated as follows from a measurementresult:

R=c×(θ_(2×Hτ1)−θ_(2×Lτ1))/(4ω_(B1))

Incidentally, in the above explanation, the distance R is calculatedtaking into account only the phase information. Amplitude is examinedbelow concerning a case in which a transmission wave having the angularfrequency ω_(C1)+ω_(B1) is used. The transmission wave indicated byEquation (1) described above delays by a delay amount τ₁=R/c at a pointin time when the transmission wave reaches a target object away from thetransmitter by the distance R. Amplitude is attenuated by attenuation L1corresponding to the distance R. The transmission wave changes to a waverx2(t) represented by the following Equation (8):

rx2(t)=L₁ cos{(ω_(C1)+ω_(B1))t+θ_(1H)−(ω_(C1)+ω_(B1))τ₁}  (8)

Further, the transmission wave is attenuated by attenuation L_(RFL) whenthe transmission wave is reflected from the target object. A reflectedwave tx2(t) in the target object is represented by the followingEquation (9):

tx2(t)=L _(RFL) L ₁ cos{(ω_(C1)+ω_(B1))t+θ _(1H)−(ω_(C1)+ω_(B1))τ₁}  (9)

The received signal rx1(t) received by the receiver is delayed by adelay amount τ₁=R/c(s) from the target object. Amplitude is attenuatedby attenuation L1 corresponding to the distance R. Therefore, thereceived signal is represented by the following Equation (10):

rx1(t)=L ₁ ×L _(RFL) ×L ₁ cos{(ω_(C1)+ω_(B1))t+θ_(1H)−2(ω_(C1)+ω_(B1))τ₁}  (10)

In this way, the transmission signal from the transmitter is attenuatedby L₁×L_(RFL)×L₁ until the transmission signal reaches the receiver.Signal amplitude that can be emitted from the transmitter in distancemeasurement needs to conform to the Radio Law according to an appliedfrequency. For example, a specific frequency in a 920 MHz band involveslimitation to suppress transmission signal power to 1 mW or less. Fromthe viewpoint of a signal-to-noise ratio of the received signal, it isnecessary to suppress attenuation between transmission and reception inorder to accurately measure a distance. However, as explained above,since attenuation is relatively large in the distance measurement formeasuring a distance using a reflected wave, a distance that can beaccurately measured is short.

Therefore, as explained above, in the present embodiment, bytransmitting and receiving signals between the two devices without usinga reflected wave, attenuation is reduced by L_(RFL)×L₁ to increase thedistance that can be accurately measured.

However, the two devices are apart from each other by the distance R andcannot share the same reference signal. In general, it is difficult tosynchronize the transmission signal with a local oscillation signal usedfor reception. That is, between the two devices, deviation occurs in asignal frequency and an initial phase is unknown. Problems in distancemeasurement performed using such an asynchronous transmission wave areexplained.

(Problems in the Case of Asynchronization)

In the distance measuring system in the present embodiment, in distancemeasurement between two objects, two devices (a first device and asecond device) that emit carrier signals (transmission signals)asynchronously from each other are disposed in the positions of therespective objects and the distance R between the two devices iscalculated. In the present embodiment, carrier signals having twofrequencies deviating from a center angular frequency ω_(C1) by theangular frequency ±ω_(B1) are transmitted in the first device. Carriersignals having two frequencies deviating from the center angularfrequency ω_(C2) by an angular frequency ±ω_(B2) are transmitted in thesecond device.

FIGS. 3A and 3B are explanatory diagrams for explaining problems in thecase in which the phase detection scheme is simply applied between twodevices A1 and A2. It is assumed that a transmission signal of thedevice A1 is received by the device A2. A local oscillator of the deviceA1 generates a signal having a frequency necessary for generating, in aheterodyne scheme, two transmission waves having carrier angularfrequencies ω_(C1)+ω_(B1) and ω_(C1)−ω_(B1). The device A1 transmits twotransmission waves having the angular frequencies. A local oscillator ofthe device A2 generates a signal having a frequency necessary forgenerating, in a heterodyne scheme, two transmission waves havingcarrier angular frequencies ω_(C2)+ω_(B2) and ω_(C2)−ω_(B2). The deviceA2 performs reception in the heterodyne scheme using the signalgenerated by the local oscillator of the device A2.

The distance between the transmission device and the reception device isrepresented as 2R to correspond to the distance in the case in which thereflected wave is used. Initial phases of a transmission signal havingthe angular frequency ω_(C1)+ω_(B1) and a transmission signal having theangular frequency ω_(C1)−ω_(B1) transmitted from the device A1 arerespectively represented as θ_(1H) and θ_(1L). Initial phases of twosignals having the angular frequencies ω_(C2)+ω_(B2) and ω_(C2)−ω_(B2)of the device A2 are respectively represented as θ_(2H) and θ_(2L).

First, a phase is considered concerning the transmission signal havingthe angular frequency ω_(C1)+ω_(B1). The transmission signal representedby Equation (1) described above is output from the device A1. Thereceived signal rx2(t) in the device A2 is represented by the followingEquation (11):

rx2(t)=cos{(ω_(C1)+ω_(B1))t+θ_(1H)−θ_(2×Hτ1)}  (11)

The device A2 multiplies together two signalscos{(ω_(C2)+ω_(B2))t+θ_(2H)} and sin{(ω_(C2)+ω_(B2))t+θ_(2H)} and areceived wave of Equation (11) to thereby separates the received waveinto an in-phase component (an I signal) and a quadrature component (a Qsignal). A phase of the received wave (hereinafter referred to asdetected phase or simply referred to as phase) can be easily calculatedfrom the I and Q signals. That is, a detected phase θ_(H1)(t) isrepresented by the following Equation (12). Note that, in the followingEquation (12), since a term of harmonics near an angular frequencyω_(C1)+ω_(c2) is removed during demodulation, the term is omitted.

θ_(H1)(t)=tan⁻¹(Q(t)/I(t))=−{(ω_(C1)−ω_(C2))t+(ω_(B1)−ω_(B2))t+θ_(1H)−θ_(2×Hτ1)}  (12)

Similarly, when the transmission signal having the angular frequencyω_(C1)−ω_(B1) is transmitted from the device A1, a detected phaseθ_(L1)(t) calculated from the I and Q signals obtained in the device A2is represented by the following Equation (13). Note that, in thefollowing Equation (13), since a term of harmonics near the angularfrequency ω_(C1)+ω_(C2) is removed during demodulation, the term isomitted.

θ_(L1)(t)=tan⁻¹(Q(t)/I(t))=−{(ω_(C1)−ω_(C2))t−(ω_(B1)−ω_(B2))t+θ_(1L)−θ_(2L)θ_(2×Lτ1)}  (13)

A phase difference between these two detected phases (hereinafterreferred to as detected phase difference or simply referred to as phasedifference) θ_(H1)(t)−θ_(L1)(t) is represented by the following Equation(14):

θ_(H1)(t)−θ_(L1)(t)=−2(ω_(B1)−ω_(B2))t+(θ_(1H)−θ_(1L))−(θ_(2H)−θ_(2L))+(θ_(2×Hτ1)−θ_(2×Lτ1))  (14)

In the distance measuring device in the past that measures a distanceusing a reflected wave, the device A1 and the device A2 are the samedevice and share the local oscillator. Therefore, the followingEquations (15) to (17) are satisfied:

ω_(B1)=ω_(B2)   (15)

θ_(1H)=θ_(2H)   (16)

θ_(1L)=θ_(2L)   (17)

When Equations (15) to (17) hold, Equation (14) is equal to Equation (7)described above. The distance R between the device A1 and the device A2can be calculated according to a phase difference calculated by I and Qdemodulation processing for the received signal in the device A2.

However, since the device A1 and the device A2 are provided to beseparated from each other and the local oscillators operateindependently from each other, Equations (15) to (17) described aboveare not satisfied. In this case, unknown information such as adifference between initial phases is included in Equation (14). Adistance cannot be correctly calculated.

(Basic Distance Measuring Method of the Embodiment)

The signals having the two angular frequencies explained abovetransmitted by the first device are received in the second device andphases of the respective signals are calculated. The signals having thetwo angular frequencies explained above transmitted by the second deviceare received in the first device and phases of the respective signalsare calculated. Further, phase information is transmitted from eitherone of the first device and the second device to the other. In thepresent embodiment, as explained below, basically the distance R betweenthe first device and the second device is calculated by adding up aphase difference between the two signals calculated by the reception ofthe first device and a phase difference between the two signalscalculated by the reception of the second device. Note that the phaseinformation may be the I and Q signals or may be information concerningphases calculated from the I and Q signals or may be informationconcerning a difference between phases calculated from two signalshaving different frequencies.

(Configuration)

In FIG. 1, the first device 1 (hereinafter referred to as device 1 aswell) and the second device 2 (hereinafter referred to as device 2 aswell) are disposed to be separated from each other by the distance R. Atleast one of the device 1 and the device 2 is movable. The distance Rchanges according to the movement. A control section 11 is provided inthe device 1. The control section 11 controls respective sections of thedevice 1. The control section 11 is configured of a processor includinga CPU. The control section 11 may operate according to a computerprogram stored in a not-shown memory and control the respectivesections.

An oscillator 13 is controlled by the control section 11 and generatesoscillation signals (local signals) having two frequencies on a basis ofa reference oscillator incorporated in the oscillator 13. The respectiveoscillation signals from the oscillator 13 are supplied to atransmitting section 14 and a receiving section 15. Angular frequenciesof the oscillation signals generated by the oscillator 13 are set toangular frequencies necessary for generating three waves ofω_(C1)+ω_(B1), ω_(C1)−ω_(B1) and ω_(C1) as angular frequencies oftransmission waves of the transmitting section 14.

The transmitting section 14 can be configured of, for example, aquadrature modulator. The transmitting section 14 is controlled by thecontrol section 11 to be capable of outputting three transmission wavesof a transmission signal having the angular frequency ω_(C1)+ω_(B1), atransmission signal having the angular frequency ω_(C1)−ω_(B1) and theangular frequency ω_(C1). The transmission waves from the transmittingsection 14 are supplied to an antenna circuit 17.

The antenna circuit 17 includes one or more antennas and can transmitthe transmission waves transmitted from the transmitting section 14. Theantenna circuit 17 receives transmission waves from the device 2explained below and supplies received signals to the receiving section15.

The receiving section 15 can be configured of, for example, a quadraturedemodulator. The receiving section 15 is controlled by the controlsection 11 to be capable of receiving and demodulating a transmissionwave from the device 2 using, for example, signals having angularfrequencies ω_(C1) and ω_(B1) from the oscillator 13 and separating andoutputting an in-phase component (an I signal) and a quadraturecomponent (a Q signal) of the received wave.

A configuration of the device 2 is the same as the configuration of thedevice 1. That is, a control section 21 is provided in the seconddevice. The control section 21 controls respective sections of thedevice 2. The control section 21 is configured of a processor includinga CPU. The control section 21 may operate according to a computerprogram stored in a not-shown memory and control the respectivesections.

An oscillator 23 is controlled by the control section 21 to generateoscillation signals having two frequencies on a basis of a referenceoscillator incorporated in the oscillator 23. The respective oscillationsignals from the oscillator 23 are supplied to a transmitting section 24and a receiving section 25. Angular frequencies of the oscillationsignals generated by the oscillator 23 are set to angular frequenciesnecessary for generating two waves of ω_(C2)+ω_(B2)and ω_(C2)−ω_(B2) asangular frequencies of transmission waves of the transmitting section24.

The transmitting section 24 can be configured of, for example, aquadrature modulator. The transmitting section 24 is controlled by thecontrol section 21 to be capable of outputting two transmission waves ofa transmission signal having an angular frequency ω_(C2)+ω_(B2) and atransmission signal having an angular frequency ω_(C2)−ω_(B2). Thetransmission waves from the transmitting section 24 are supplied to anantenna circuit 27.

The antenna circuit 27 includes one or more antennas and can transmitthe transmission waves transmitted from the transmitting section 24. Theantenna circuit 27 receives transmission waves from the device 1 andsupplies received signals to the receiving section 25.

The receiving section 25 can be configured of, for example, a quadraturedemodulator. The receiving section 25 is controlled by the controlsection 21 to be capable of receiving and demodulating a transmissionwave from the device 1 using, for example, signals having angularfrequencies ω_(C2) and ω_(B2) from the oscillator 23 and separating andoutputting an in-phase component (an I signal) and a quadraturecomponent (a Q signal) of the received wave.

FIG. 4 is a circuit diagram showing an example of specificconfigurations of the transmitting section 14 and the receiving section15 shown in FIG. 1. FIG. 5 is a circuit diagram showing an example ofspecific configurations of the transmitting section 24 and the receivingsection 25 shown in FIG. 1. FIGS. 4 and 5 show a transceiver of an imagesuppression scheme. However, the transceiver is not limited to theconfiguration.

Note that a configuration of the image suppression scheme is publiclyknown. As characteristics of the image suppression scheme, when a higherangular frequency band is demodulated centering on a local angularfrequency for a high frequency, that is, ω_(C1) or ω_(C2), a signal in alower angular frequency band is attenuated and, when a lower angularfrequency band is demodulated, a signal in a higher angular frequencyband is attenuated. This filtering effect is due to signal processing.The same applies to transmission. When the higher angular frequency bandis demodulated centering on ω_(C1) or ω_(C2), sin(ω_(B1)+θ_(B1)) orsin(ω_(B2)t+θ_(B2)) shown in FIGS. 4 and 5 is used. When the lowerangular frequency band is demodulated, −sin(ω_(B1)t+θ_(B1)) or−sin(ω_(B2)t+θ_(B2)) shown in FIGS. 4 and 5 is used. The frequency banddemodulated is decided by change of such polarity.

Note that, in a receiver of the image suppression scheme, a term ofharmonics near the angular frequency ω_(C2)+ω_(C2) is removed duringdemodulation. Therefore, in an operation explained below, this term isomitted.

The transmitting section 14 is configured of multipliers TM11 and TM12and an adder TS11. Oscillation signals having an angular frequencyω_(C1) and having phases 90 degrees different from each other arerespectively given to the multipliers TM11 and TM12 from the oscillator13. Oscillation signals having an angular frequency ω_(B1) and havingphases 90 degrees different from each other are respectively given tothe multipliers TM11 and TM12 from the oscillator 13. An inverted signalof the oscillation signal having the angular frequency ω_(B1) is alsogiven to the multiplier TM12 from the oscillator 13.

The multipliers TM11 and TM12 respectively multiply together the twoinputs and give multiplication results to the adder TS11. The adder TS11adds up outputs of the multipliers TM11 and TM12 and outputs an additionresult as a transmission wave tx1.

The receiving section 15 is configured of multipliers RM11 to RM16 andadders RS11 and RS12. A transmission wave of the device 2 is input tothe multipliers RM11 and RM12 via the antenna circuit 17 as a receivedsignal rx1. Oscillation signals having the angular frequency ω_(C1) andphases 90 degrees different from each other are respectively given tothe multipliers RM11 and RM12 from the oscillator 13. The multiplierRM11 multiplies together the two inputs and gives a multiplicationresult to the multipliers RM13 and RM14. The multiplier RM12 multipliestogether the two inputs and gives a multiplication result to themultipliers RM15 and RM16.

An oscillation signal having the angular frequency (a local angularfrequency for baseband processing) ω_(B1) is given to the multipliersRM13 and RM15 from the oscillator 13. The multiplier RM13 multipliestogether the two inputs and gives a multiplication result to the adderRS11. The multiplier RM14 multiplies together the two inputs and gives amultiplication result to the adder RS12.

An oscillation signal having the angular frequency ω_(B1) or an invertedsignal of the oscillation signal, that is, a signal orthogonal to theoscillation signal having the angular frequency ω_(B1) given to themultiplier RM13 is given to the multipliers RM14 and RM16 from theoscillator 13. The multiplier RM14 multiplies together the two inputsand gives a multiplication result to the adder RS12. The multiplier RM16multiplies together the two inputs and gives a multiplication result tothe adder RS11.

The adder RS11 adds up outputs of the multipliers RM13 and RM16 andoutputs an addition result as an I signal. The adder RS12 adds upoutputs of the multipliers RM14 and RM15 and outputs an addition resultas a Q signal. The I and Q signals from the receiving section 15 aresupplied to the control section 11.

The circuits shown in FIGS. 4 and 5 are the same circuit. That is, inFIG. 5, the configurations of the multipliers TM21, TM22, and RM21 toRM26 and the adders TS21, RS21, and RS22 are respectively the same asthe configurations of the multipliers TM11, TM12, and RM11 to RM16 andthe adders TS11, RS11, and RS12 shown in FIG. 4. The configurations areonly different in that, since the frequency and the phase of theoscillation signal of the oscillator 23 are different from the frequencyand the phase of the oscillation signal of the oscillator 13, in FIG. 5,a local angular frequency for baseband ω_(B2) is input instead of theangular frequency ω_(B1) shown in FIG. 4 and ω_(C2) is input instead ofthe angular frequency ω_(C1) shown in FIG. 4. The I and Q signals fromthe receiving section 25 are supplied to the control section 21.

In the present embodiment, the control section 11 of the device 1controls the transmitting section 14 to transmit two transmission waveshaving angular frequencies ω_(C1)+ω_(B1) and ω_(C1)−ω_(B1) via theantenna circuit 17.

On the other hand, the control section 21 of the device 2 controls thetransmitting section 24 to transmit two transmission waves havingangular frequencies ω_(C2)+ω_(B2) and ω_(C2)−ω_(B2) via the antennacircuit 27.

The control section 11 of the device 1 controls the receiving section 15to receive the two transmission waves from the device 2 and acquires theI and Q signals. The control section 11 calculates a difference betweentwo phases calculated from the I and Q signals respectively obtained bytwo received signals.

Similarly, the control section 21 of the device 2 controls the receivingsection 25 to receive the two transmission waves from the device 1 andacquires the I and Q signals. The control section 21 calculates adifference between two phases calculated from the I and Q signalsrespectively obtained by two received signals.

In the present embodiment, the control section 11 of the device 1 givesphase information based on the acquired I and Q signals to thetransmitting section 14 and causes the transmitting section 14 totransmit the phase information. Note that, as explained above, as thephase information, for example, a predetermined initial value may begiven. The phase information may be I and Q signals calculated from thetwo received signals, may be information concerning phases calculatedfrom the I and Q signals, or may be information concerning a differencebetween the phases.

For example, the control section 11 may generate I and Q signals basedon phase information of a received signal having an angular frequencyω_(B2) and supplies the I and Q signals respectively to the multipliersTM11 and TM12 to transmit the phase information.

During output of the oscillation signal having the angular frequencyω_(B1), the control section 11 may generate I and Q signals obtained byadding phase information of the received signal having the angularfrequency ω_(B2) to an initial phase of the oscillation signal havingangular frequency ω_(B1) and supply the I and Q signals respectively tothe multipliers TM11 and TM12 to transmit the phase information.

The receiving section 25 of the device 2 receives the phase informationtransmitted by the transmitting section 14 via the antenna circuit 27.The receiving section 25 demodulates a received signal and obtains I andQ signals of the phase information. The I and Q signals are supplied tothe control section 21. The control section 21 obtains, according to thephase information from the receiving section 25, a value including thephase difference acquired by the control section 11 of the device 1. Thecontrol section 21 functioning as a calculating section adds up thephase difference obtained by the reception result of the receivingsection 25 and the phase difference based on the phase informationtransmitted from the device 2 to calculate the distance R between thefirst device 1 and the second device 2.

Note that, in FIG. 1, an example is shown in which both of the firstdevice 1 and the second device 2 have a function of transmitting phaseinformation and a function of giving received phase information to thecontrol section and calculating the distance R. However, it issufficient that one of the first device 1 and the second device 2 hasthe function of transmitting phase information and the other has thefunction of giving received phase information to the control section andcalculating the distance R.

(Explanation of Distance Measurement in Which Two Waves are Used)

An operation of the distance measuring system is explained withreference to the flowchart of FIG. 6 concerning a case in which twowaves are used. In FIG. 6, an operation of the device 1 is shown on aleft side and an operation of the device 2 is shown on a right side. InFIG. 6, an arrow connecting steps of the devices 1 and 2 indicates thatcommunication is performed between the devices 1 and 2. Note that stepsS4, S5, S14, and S15 are substantially simultaneously executed.

In step S1, the control section 11 of the device 1 determines whether aninstruction for a distance measurement start is received. When theinstruction for the distance measurement start is received, the controlsection 11 controls the oscillator 13 to start an output of a necessaryoscillation signal. In step S11, the control section 21 of the device 2determines whether an instruction for a distance measurement start isreceived. When the instruction for the distance measurement start isreceived, the control section 21 controls the oscillator 23 to start anoutput of a necessary oscillation signal.

Note that, as explained below, in step S9, the control section 11 endsoscillation. In step S20, the control section 21 ends oscillation.Control of a start and an end of oscillation in the control sections 11and 21 indicates that oscillation of the oscillators 13 and 23 is notstopped during transmission and reception periods for distancemeasurement. Actual start and end timings of the oscillation are notlimited to the flow shown in FIG. 6. In a period in which theoscillation of the oscillators 13 and 23 continues, initial phases ofthe respective oscillators 13 and 23 are not set anew.

The control section 11 of the device 1 generates two transmissionsignals in step S3 and causes the antenna circuit 17 to transmit thetransmission signals as transmission waves (step S4). The controlsection 21 of the device 2 generates two transmission signals in stepS13 and causes the antenna circuit 27 to transmit the transmissionsignals as transmission waves (step S14).

It is assumed that an initial phase of an oscillation signal having thefrequency ω_(C1) output from the oscillator 13 of the device 1 is θ_(c1)and an initial phase of an oscillation signal having the frequencyω_(B1) is θ_(B1). Note that, as explained above, the initial phasesθ_(c1) and θ_(B1) are not set anew as long as the oscillation of theoscillator 13 continues.

Note that it is assumed that an initial phase of an oscillation signalhaving the frequency ω_(C2) output from the oscillator 23 of the device2 is θ_(c2) and an initial phase of an oscillation signal having thefrequency ω_(B2) is θ_(B2). The initial phases θ_(c2) and θ_(B2) are notset anew as long as the oscillation of the oscillator 23 continues.

Note that, when simultaneous transmission and simultaneous reception oftwo frequencies are assumed, two wireless sections shown in FIG. 4 arenecessary in the device 1 and two wireless sections shown in FIG. 5 arenecessary in the device 2. Alternatively, a radio of a superheterodynescheme or the like is used. However, the respective oscillators use thesame radio section.

(Transmission and Reception of a Transmission Wave Having the AngularFrequency ω_(C1)+ω_(B1) from the Device 1)

Two transmission waves having the angular frequencies ω_(C1)+ω_(B1) andω_(C1)−ω_(B1) are output from the transmitting section 14 of the device1, and the transmitting section 14 is composed of the multipliers TM11and TM12 and the adder TS11. The transmission signal tx1(t) having theangular frequency ω_(C1)+ω_(B1) is represented by the following Equation(18):

tx1(t)=cos(ω_(C1)+θ_(C1))cos(ω_(B1) t+θ_(B1))−sin(ω_(C1) t+θ_(c1))sin(ω_(B1) t+θ _(B1))=cos{(ω_(C1)+ω_(B1))t+θ _(C1)+θ_(B1)}  (18)

When the distance between the devices 1 and 2 is represented as R and adelay until a transmission wave from the device 1 is received by thedevice 2 is represented as τ₁, the received signal rx2(t) of the device2 can be represented by the following Equations (19) and (20):

rx2(t)=cos{(ω_(C1)+ω_(B1))(t−τ ₁)+θ_(C1)+θ_(B1)}=cos{(ω_(C1)+ω_(B1))t+θ_(C1)+θ_(B1)−θ_(τH1)}  (19)

θ_(τH1)=(ω_(C1)+ω_(B1))τ₁   (20)

The received signal rx2(t) is received by the antenna circuit 27 andsupplied to the receiving section 25. In the receiver shown in FIG. 5,the received signal rx2(t) is input to the multipliers RM21 and RM22.Subsequently, signals in respective nodes of the receiver shown in FIG.5 are sequentially calculated. Outputs of the multipliers RM21, RM23,and RM24 are respectively represented as I₁(t), I₂(t), and I₃(t),outputs of the multipliers RM22, RM26, and RM25 are respectivelyrepresented as Q₁(t), Q₂(t), and Q₃(t), and outputs of the adders RS21and RS22 are respectively represented as I(t) and Q(t). The outputs arerepresented by the following Equations (21) to (26):

I ₁(t)=cos(ω_(C2) t+θ _(C2))×cos{(ω_(C1)+ω_(B1))t+θ_(c1)+θ_(B1)−θ_(τH1)}  (21)

Q ₁(t)=sin(ω_(C2) t+θ _(C2))×cos{(ω_(C1)+ω_(B1))t+θ_(c1)+θ_(B1)−θ_(τH1)}  (22)

I ₂(t)=I ₁(t)×cos(ω_(B2) t+θ _(B2))   (23)

Q ₂(t)=Q ₁(t)×sin(ω_(B2) t+θ _(B2))   (24)

I ₃(t)=I ₁(t)×sin(ω_(B2) t+θ _(B2))   (25)

Q ₃(t)=Q ₁(t)×cos(ω_(B2) t+θ _(B2))   (26)

An output I(t) of the adder RS21 is I(t)=I₂(t)+Q₂(t). An output Q(t) ofthe adder RS22 is Q(t)=I₃(t)−Q3(t). A phase θ_(H1)(t) obtained from I(t)and Q(t) is represented by the following Equation (27):

θ_(H1)(t)=tan⁻¹(Q(t)/I(t))=−{(ω_(C1)−ω_(C2))t+(ω_(B1)−ω_(B2))t+θ_(C1)−θ_(C2)+θ_(B1)−θ_(B2)−θ_(τH1)}  (27)

(Transmission and Reception of a Transmission Wave Having the AngularFrequency ω_(C2)+ω_(B2) from the Device 2)

Similarly, when the signal tx2(t) having the angular frequencyω_(C2)+ω_(B2) transmitted from the device 2 is received by the device 1after a delay τ₂, a phase θ_(H2)(t) obtained from the signals I(t) andQ(t) detected by the device 1 is calculated.

tx2(t)=cos(ω_(C2)+θ_(C2))cos(ω_(B2) t+θ _(B2))−sin(ω_(C2) t +θ_(c2))sin(ω_(B2) t+θ _(B2))=cos{(ω_(C2)+ω_(B2))t+θ _(C2)+θ_(B2)}  (28)

rx1(t)=cos{(ω_(C2)+ω_(B2))(t−τ ₂)+θ_(C2)+θ_(B2)}=cos{(ω_(C2)+ω_(B2))t+θ_(C2)+θ_(B2)+θ_(τH2)}  (29)

θ_(τH2)=(ω_(C2)+ω_(B2))τ₂   (30)

The received signal rx1(t) is received by the antenna circuit 17 andsupplied to the receiving section 15. In the receiver shown in FIG. 4,the received signal rx1(t) is input to the multipliers RM11 and RM12.Subsequently, signals in respective nodes of the receiver shown in FIG.4 are sequentially calculated. Outputs of the multipliers RM11, RM13,and RM14 are respectively represented as I₁(t), I₂(t), and I₃(t),outputs of the multipliers RM12, RM16, and RM15 are respectivelyrepresented as Q₁(t), Q₂(t), and Q₃(t), and outputs of the adders RS11and RS12 are respectively represented as I(t) and Q(t). The outputs arerepresented by the following Equations (31) to (36):

I ₁(t)=cos(ω_(C1) t+θ _(C1))×cos{(ω_(C2)+ω_(B2))t+θ_(c2)+θ_(B2)−θ_(τH2)}  (31)

Q ₁(t)=sin(ω_(C1) t+θ _(C1))×cos{(ω_(C2)+ω_(B2))t+θ_(c2)+θ_(B2)−θ_(τH2)}  (32)

I ₂(t)=I ₁(t)×cos(ω_(B1) t+θ _(B1))   (33)

Q ₂(t)=Q ₁(t)×sin(ω_(B1) t+θ _(B1))   (34)

I ₃(t)=I ₁(t)×sin(ω_(B1) t+θ _(B1))   (35)

Q ₃(t)=Q ₁(t)×cos(ω_(B1) t+θ _(B1))   (36)

An output I(t) of the adder RS11 is I(t)=I₂(t)+Q₂(t). An output Q(t) ofthe adder RS12 is Q(t)=I₃(t)−Q₃(t). A phase θ_(H2)(t)=tan⁻¹(Q(t)/I(t))obtained from I(t) and Q(t) is represented by the following Equation(37):

θ_(H2)(t)=(ω_(C1)−ω_(C2))t+(ω_(B1)−ω_(B2))t+θ_(C1)−θ_(C2)+θ_(B1)−θ_(B2)+θ_(τH2)   (37)

(Transmission and Reception of a Transmission Wave Having the AngularFrequency ω_(C1)−ω_(B1) from the Device 1)

The signal tx1(t) having the angular frequency ω_(C1)−ω_(B1) transmittedfrom the device 1 is calculated in the same manner.

tx1(t)=cos(ω_(C1)+θ_(C1))cos(ω_(B1) t+θ_(B1))−sin(ω_(C1) t+θ_(c1))sin(ω_(B1) t+θ _(B1))=cos{(ω_(C1)−ω_(B1))t+θ _(C1)=θ_(B1)}  (38)

Since the distance between the devices 1 and 2 is R and the delay timeis τ₁, the received signal rx2(t) in the device 2 is represented by thefollowing Equations (39) and (40):

rx2(t)=cos{(ω_(C1)−ω_(B1))(t−τ ₁)+θ_(C1)−θ_(B1)}=cos{(ω_(C1)−ω_(B1))t+θ_(C1)−θ_(B1)−θ_(τL1)}  (39)

θ_(τL1)=(ω_(C1)−ω_(B1))τ₁   (40)

Signals of the respective nodes of the device 2 can be represented bythe following Equations (41) to (47):

I ₁(t)=cos(ω_(C2) t+θ _(C2))×cos{(ω_(C1)−ω_(B1))t+θ_(c1)−θ_(B1)−θ_(τL1)}  (41)

Q ₁(t)=sin(ω_(C2) t+θ _(C2))×cos{(ω_(C1)−ω_(B1))t+θ_(c1)−θ_(B1)−θ_(τL1)}  (42)

I ₂(t)=I ₁(t)×cos(ω_(B2) t+θ _(B2))   (43)

Q ₂(t)=Q ₁(t)×−sin(ω_(B2) t+θ _(B2))   (44)

I ₃(t)=I ₁(t)×−sin(ω_(B2) t+θ _(B2))   (45)

Q ₃(t)=Q ₁(t)×cos(ω_(B2) t+θ _(B2))   (46)

A phase θ_(H1)(t)=tan⁻¹(Q(t)/I(t)) detected by the device 2 fromI(t)=I₂(t)-Q₂(t) obtained from the adder RS21 and Q(t)=I₃(t)+Q₃(t)obtained from the adder RS22 is represented by the following Equation(47):

θ_(L1)(t)=tan⁻¹(Q(t)/I(t))=−{(ω_(C1)−ω_(C2))t−(ω_(B1)−ω_(B2))t+θ_(C1)−θ_(C2)−(θ_(B1)−θ_(B2))−θ_(τL1)}  (47)

(Transmission and Reception of a Transmission Wave Having the AngularFrequency ω_(C2)−ω_(B2) from the device 2)

Similarly, when the signal tx2(t) having the angular frequencyω_(C2)−ω_(B2) transmitted from the device 2 is received by the device 1after a delay τ₂, a phase θ_(L2)(t) obtained from I(t) and Q(t) detectedby the device 1 is calculated.

tx2(t)=cos(ω_(C2)+θ_(C2))cos(ω_(B2) t+θ _(B2))+sin(ω_(C2) t +θ_(C2))sin(ω_(B2) t+θ _(B2))=cos{(ω_(C2)+ω_(B2))t+θ _(C2)−θ_(B2)}  (48)

rx1(t)=cos{(ω_(C2)−ω_(B2))(t−τ ₂)+θ_(C2)−θ_(B2)}=cos{(ω_(C2)−ω_(B2))t+θ_(C2)−θ_(B2)−θ_(τL2)}  (49)

θ_(τL2)=(ω_(C2)−ω_(B2))τ₂   (50)

Signals of the respective nodes of the device 1 can be represented bythe following Equations (53) to (57):

I ₁(t)=cos(ω_(C1) t+θ _(C1))×cos{(ω_(C2)−ω_(B2))t+θ_(c2)−θ_(B2)−θ_(τL2)}  (51)

Q ₁(t)=sin(ω_(C1) t+θ _(C1))×cos{(ω_(C2)−ω_(B2))t+θ_(c2)−θ_(B2)−θ_(τL2)}  (52)

I ₂(t)=I ₁(t)×cos(ω_(B1) t+θ _(B1))   (53)

Q ₂(t)=Q ₁(t)×−sin(ω_(B1) t+θ _(B1))   (54)

I ₃(t)=I ₁(t)×−sin(ω_(B1) t+θ _(B1))   (55)

Q ₃(t)=Q ₁(t)×cos(ω_(B1) t+θ _(B1))   (56)

A phase θ_(H1)(t)=tan⁻¹(Q(t)/I(t)) detected by the device 1 fromI(t)=I₂(t)-Q₂(t) obtained from the adder RS11 and Q(t)=I₃(t)+Q₃(t)obtained from the adder RS12 is represented by the following Equation(57):

θ_(L2)(t)=(ω_(C1)−ω_(C2))t−(ω_(B1)−ω_(B2))t+θ_(C1)−θ_(C2)−(θ_(B1)−θ_(B2))+θ_(τL2)   (57)

In step S6 in FIG. 6, the control section 11 of the device 1 acquiresthe I and Q signals received by the receiving section 15. In step S7,the control section 11 calculates the phases θ_(τH1)(t) and θ_(τL1)(t)represented by Equations (27) and (47) described above. In step S16 inFIG. 6, the control section 21 of the device 2 acquires the I and Qsignals received by the receiving section 25. In step S17, the controlsection 21 calculates the phases θ_(τH2)(t) and θ_(τL2)(t) representedby Equations (37) and (57) described above.

The control section 11 gives acquired phase information to thetransmitting section 14 and causes the transmitting section 14 totransmit the phase information (step S8). For example, the controlsection 11 supplies the I and Q signals based on the phase informationinstead of the oscillation signals supplied to the multipliers TM11 andTM12 shown in FIG. 4. As described later, the phase information aregiven to I_(T), Q_(T) signals in FIG. 50 and FIG. 51. Note that anothertransmitter for transmitting the phase information may be used.

In step S18, the control section 21 of the device 2 receives the phaseinformation from the device 1. As explained above, the phase informationmay be the I and Q signals from the receiving section 15 of the device1, may be information concerning phases obtained from the I and Qsignals, or may be information concerning a difference between thephases.

In step S19, the control section 21 performs an operation of thefollowing Equation (58) to calculate a distance. The following Equation(58) is an equation for adding up a difference between Equation (27) andEquation (47) and a difference between Equation (37) and Equation (57).

{θ_(H1)(t)−θ_(L1)(t)}+{θ_(H2)(t)−θ_(L2)(t)}=(θ_(τH1)−θ_(τL1))+(θ_(τH2)−θ_(τL2))  (58)

The following Equations (59) and (60) hold:

θ_(τH1)−θ_(τL1)=(ω_(C1)+ω_(B1))τ₁−(ω_(C1)−ω_(B1))τ₁=2ω_(B1τ1)   (59)

θ_(τH2)−θ_(τL2)=(ω_(C2)+ω_(B2))τ₂−(ω_(C2)−ω_(B2))τ₂=2ω_(B2τ2)   (60)

The delays τ₁ and τ₂ of radio waves between the devices 1 and 2 are thesame irrespective of a traveling direction. Therefore, the followingEquation (61) is obtained from Equation (58):

{θ_(H1)(t)−θ_(L1)(t)}+{θ_(H2)(t)−θ_(L2)(t)}=(θ_(τH1)−θ_(τL1))+(θ_(τH2)−θ_(τL2))=2×(ω_(B1)+ω_(B2))τ₁  (61)

Equation (61) described above indicates that a value proportional to adouble of the distance R is calculated by addition of a phase differencebetween two frequencies by the I and Q signals detected by the device 2and a phase difference between two frequencies by the I and Q signalsdetected by the device 1. In general, the angular frequency ω_(B1) bythe oscillator 13 of the device 1 and the angular frequency ω_(B2) bythe oscillator 13 of the device 2 can be matched with an error in theorder of several ten ppm. Therefore, the distance R by Equation (61)described above can be calculated at resolution of equal to or higherthan at least approximately 1 m.

In step S9, the control section 11 stops the oscillator 13. In step S20,the control section 21 stops the oscillator 23. Note that, as explainedabove, the control sections 11 and 21 only have to continue theoscillation in a period of transmission and reception in steps S4, S5,S14, and S15. Start and end timings of the oscillation of theoscillators 13 and 23 are not limited to the example shown in FIG. 6.

(Calculation of a Distance by a Residue of 2π)

Incidentally, when the addition of the phase differences detected by thedevice 1 and the device 2 is performed, a result of the addition issometimes equal to or smaller than −π(rad) or larger than π(rad). Inthis case, it is possible to calculate a correct distance R with respectto a detected phase by calculating a residue of 2π.

FIGS. 7 and 8 are explanatory diagrams for explaining a method ofcalculating a distance using a system of residue.

For example, when R=11 m and ω_(B1)=ω_(B2)=2π×5M, a detected phasedifference Δθ₁₂ obtained by the device 1 and a detected phase differenceΔθ₂₁ obtained by the device 2 are respectively as represented by thefollowing Equations (62) and (63):

Δθ₁₂=θ_(τH1)−θ_(τL1)=−1.8849   (62)

Δθ₂₁=θ_(τH2)−θ_(τL2)=−6.0737   (63)

The following Equation (61a) is obtained from Equation (61) describedabove:

(1/2)[{Δθ₁₂}+{Δθ₂₁}]=(ω_(B1)+ω_(B2))(R/c)   (61a)

FIG. 7 shows a phase relation between Equations (62) and (63) describedabove. A phase of a sum of Δθ₂₁ indicated by an arrow on inner most sideand Δθ₁₂ indicated by a second arrow from the inner side rotating in aclockwise direction on a basis of a phase 0 degree is a phase indicatedby a third arrow from the inner side. A half angle of this phase is aphase of a thick line indicated by an arrow on the outermost side.

From Equation (61a), −0.3993=(ω_(B1)+ω_(B2))(R/c) is obtained. When thisequation is solved, R=−19 m. It is shown that a distance cannot becorrectly calculated because a detected phase difference is larger than−π(rad).

Therefore, in the present embodiment, in such a case, as shown in FIG.8, 27π is added to both of Δθ₁₂ and Δθ₂₁. That is, a phase of a sum of2π+Δθ₂₁ indicated by an arrow on inner most side and 2π+Δθ₁₂ indicatedby a second arrow from the inner side rotating in a counterclockwisedirection on a basis of the phase 0 degree is a phase indicated by athird arrow from the inner side. A half angle of this phase is a phaseof a thick line indicated by an arrow on the outermost side.

2π+(Δθ₁₂+Δθ₂₁)/2=2.3008

-   From Equation (61a), R is calculated as R=11 m.

Consequently, in the present embodiment, when the detected phasedifferences are added up, a residue of 2π only has to be calculated tocalculate the distance R. Note that the method of using the residue of2π in the phase addition is applicable in other examples explainedbelow.

(Selection From a Plurality of Distance Candidates)

Incidentally, a detected phase difference exceeding 2π cannot bedetected. Therefore, a plurality of distance candidates are present withrespect to a calculated detected phase difference. As a method ofselecting a correct distance from the plurality of distance candidates,a method of transmitting three transmission waves having differentangular frequencies and a method of determining a distance according toreceived power exist.

FIG. 9 is an explanatory diagram showing an example in which a distanceis plotted on the horizontal axis and a phase is plotted on the verticalaxis and the third transmission wave having a different angularfrequency are transmitted.

The following Equation (64) is obtained from Equation (61) describedabove:

(1/2)×{(θ_(τH1)−θ_(τL1))+(θ_(τH2)−θ_(τL2))}=(ω_(B1)+ω_(B2))×(R/c)   (64)

When a left side is described as θ_(det), a relation between thedistance R and θ_(det) is as indicated by a solid line in FIG. 9.However, although a sum θ_(det) of detected phase differences calculatedby Equation (64) described above can take a value other than a valuebetween −π(rad) and π(rad), the sum θ_(det) of the phase differences isa value converted into a value between −π(rad) and π(rad). In general,this is because a phase angle is displayed within a range [−π(rad),π(rad)].

Referring to FIG. 9, candidates of a distance by the sum O_(det) of thedetected phase differences include R₁, R₂, and R₃. The sum θ_(det) ofthe detected phase differences is an addition and subtraction result ofphases obtained by transmission and reception of respective transmissionwaves having angular frequencies ω_(C1)+ω_(B1), ω_(C1)−ω_(B1),ω_(C2)+ω_(B2) and ω_(C2)−ω_(B2). However, an addition and subtractionresult of phases obtained by transmission and reception of transmissionwaves having angular frequencies ω_(C1)+ω_(B1)/Q and ω_(C2)+ω_(B2)/Q isconsidered anew. Q is a rational number satisfying the followingInequality (65):

Q>1   (65)

A relation between detected phases at the new angular frequencies andthe distance R can be indicated by a broken line shown in FIG. 9. Toselect a correct distance from the candidates R₁, R₂, and R₃ of thedistance, a result of the detected phases obtained at the new angularfrequencies is referred to. That is, if θ_(det)1 is detected, thecorrect distance is determined as the distance R₁. If θ_(det)2 isdetected, the correct distance is determined as the distance R₂. Notethat, if a coverage of a radio wave is kept small, the inspection by thephase aliasing is unnecessary. Note that the transmission at thedifferent three frequencies is explained above. However, the same can berealized by transmitting different three or more frequencies.

A method of selecting a correct distance according to amplitudeobservation of a detected signal is explained with reference to theexplanatory diagram of FIG. 10.

In Equation (8) described above, the amplitude is attenuated at theattenuation L₁ according to the distance R. However, propagationattenuation in a free space is represented by the following Equation(66):

L ₁=(λ/4πR)²   (66)

where λ is a wavelength. According to Equation (66), if the distance Ris large, the attenuation L₁ is also large and, if the distance R issmall, the attenuation L1 is also small. FIG. 10 shows this relation.When it is assumed that an antenna gain of transmission and reception is1 and transmission power is P₀, received power P₁ at the distance R₁ andreceived power P₂ at the distance R₂ are respectively represented by thefollowing Equations (67) and (68):

P ₁=(λ/4πR ₁)² ×P ₀   (67)

P ₂=(λ/4πR ₂)² ×P ₀   (68)

It is possible to distinguish the distances R₁ and R₂ from the sumθ_(det) of the detected phase differences and the received power.

Note that, in this case, it is possible to perform sure distancemeasurement by using the residue of 2π in the phase addition as well.

In this way, in the present embodiment, basically, two transmissionwaves are adopted in each of the first device and the second device.Each of the first device and the second device transmits signals havingtwo angular frequencies to each of the second device and the firstdevice. Each of the first and second devices calculates two phases oftwo received signals having different angular frequencies. Any one ofthe first device and the second device transmits calculated phaseinformation to the other. The device that receives the phase informationaccurately calculates the distance between the first device and thesecond device irrespective of initial phases of the oscillators of thefirst device and the second device according to an addition result aphase difference between the two received signals received by the firstdevice and a phase difference between the two received signals receivedby the second device. In the distance measuring system, a reflected waveis not used. The accurate distance measurement is performed by only onedirection from the first device and the second device. It is possible toincrease a measurable distance.

(Problems in the Time-Series Transmission and Reception)

In the explanation described above, Equation (61) described above forcalculating a distance from addition of detected phase differences iscalculated assuming that the delays τ₁ and τ₂ of the radio wave are thesame in Equation (58) described above. However, Equation (58) is anexample in the case in which transmission and reception processing issimultaneously performed in the devices 1 and 2.

However, because of the provision of the Radio Law in the country, afrequency band in which simultaneous transmission and reception cannotbe performed is present. For example, a 920 MHz band is an example ofthe frequency band. When distance measurement is performed in such afrequency band, transmission and reception has to be performed in timeseries.

FIG. 11A is a flowchart in time-series transmission and reception. FIGS.11B to 15 are explanatory diagrams for explaining problems in thetime-series transmission and reception and a method of solving theproblems.

When it is specified that only one wave can be transmitted and receivedat the same time between the devices 1 and 2, it is necessary to carryout, in time-series processing, transmission and reception of at leastfour waves necessary for distance measurement. However, when thetime-series transmission and reception is carried out, a phaseequivalent to a delay that occurs in time-series processing is added toa detected phase. A phase required for propagation cannot be calculated.A reason for this is explained by modifying Equation (58) explainedabove.

Note that a broken line portion of FIG. 6 is substantiallysimultaneously executed. However, when transmission and reception of onewave is performed at a time in time-series processing, the broken lineportion is as shown in FIG. 11A.

As in the explanation described above, in the devices 1 and 2 separatedfrom each other by the distance R, a phase (shift amount) at the timewhen a signal having the angular frequency ω_(C1)+ω_(B1) transmittedfrom the device 1 is detected in the device 2 is represented as θ_(H1),a phase at the time when a signal having the angular frequencyω_(C1)−ω_(B1) transmitted from the device 1 is detected in the device 2is represented as θ_(L1), a phase (shift amount) at the time when asignal having the angular frequency ω_(C2)+ω_(B2) transmitted from thedevice 2 is detected in the device 1 is represented as θ_(H2), and aphase at the time when a signal having the angular frequencyω_(C2)−ω_(B2) transmitted from the device 2 is detected in the device 1is represented as θ_(L2).

For example, phase detection order is set as θ_(H1), θ_(L2), θ_(H2), andθ_(L1). As shown in FIGS. 11B and 11C, respective transmission signalsare transmitted and received while being shifted by a time T. In thiscase, a time period is substituted in (t) of Equations (27), (37), (47),and (57) described above. The following Equation (120) obtained bymodifying Equation (58) described above holds:

{θ_(H1)(t)−θ_(L1)(t+3T)}+{θ_(H2)(t+2T)−θ_(L2)(t+T)}=(θ_(τH1)−θ_(τL1))+(θ_(τH2)−θ_(τL1))+(ω_(C1)−ω_(C2))4T  (120)

A last term of Equation (120) described above is a phase added by thetime-series transmission and reception. The added phase is amultiplication result of error angular frequencies between the localangular frequencies used in the device 1 and the device 2 and a delay4T, where the local frequencies are almost the same frequencies as theRF frequencies used in the device 1 and the device 2. When a localfrequency is set to 920 MHz, a frequency error is set to 40 ppm, and adelay T is set to 0.1 ms, the added phase is 360°×14.7. It is shown thatan error due to the added phase is too large and distance measurementcannot be correctly performed.

The phase detection order is set as θ_(H1), θ_(L1), θ_(H2), and θ_(L2).FIGS. 12A and 12B show an example of this case. In this case, thefollowing Equation (121) is obtained by modifying Equation (58)described above:

{θ_(H1)(t)−θ_(L1)(t+T)}+{θ_(H2)(t+2T)=θ₂(t+3T)}=(θ_(τH1)−θ_(τL1))+(θ_(τH2)−θ_(τL2))+(ω_(B1)−ω_(B2))4T  (121)

A last term of Equation (121) described above is a phase added by thetime-series transmission and reception. The added phase is amultiplication result of error angular frequencies between the localangular frequencies for baseband processing used in the device 1 and thedevice 2 and a delay 4T, where the local frequencies for basebandprocessing are almost the same frequencies as the baseband frequencies 0used in the device 1 and the device 2. When a local frequency forbaseband processing is set to 5 MHz, a frequency error is set to 40 ppm,and the delay T is set to 0.1 ms, the added phase is 360°×0.08=28.8°. Itis shown from precedence that distance measurement can be correctlyperformed.

However, in this case, it depends on a system whether an error is withinan allowable error of system specifications. The present embodimentpresents a time-series procedure for reducing a distance error thatoccurs because of the time-series transmission and reception. Note thatthe present embodiment indicates a procedure that takes into account theregulation of transmission and reception specified by the Radio Law.

(Specific Procedure)

First, an influence due to a transmission delay is considered.

The following Equation (122) is obtained by modifying Equation (58)described above:

{θ_(H1)(t)+θ_(H2)(t)}−{θ_(L1)(t)+θ_(L2)(t)}=(θ_(τH1)+θ_(τH2))−(θ_(τL1)+θ_(τL2))  (122)

In the equation,

θ_(H1)(t)+θ_(H2)(t)=θ_(τH1)−θ_(τH2)   (123)

θ_(L1)(t)+θ_(L2)(t)=θ_(τL1)+θ_(τL2)   (124)

In wireless communication, there is a provision that, when a signaladdressed to oneself is received, a reply can be transmitted withoutcarrier sense. According to the provision, after transmission of asignal from the device 1 to the device 2 ends, a reply is immediatelytransmitted from the device 2 to the device 1. To simplify an analysis,it is assumed that the device 2 transmits a reply to the device 1 afterto from the transmission by the device 1. The following Equation (125)is obtained from Equations (27) and (37):

θ_(H1)(t)+θ_(H2)(t+t₀)=θ_(τH1)+θ_(τH2)+{(ω_(B1)−ω_(B2))+(ω_(C1)−ω_(C2))}t ₀   (125)

A delay t₀ is a shortest time period and includes a time period in whicha signal having the angular frequency ω_(C1)+ω_(B1) is transmitted fromthe device 1 to the device 2, a transmission and reception timingmargin, and a propagation delay. A third term and a fourth term on aright side are phase errors due to the delay to. The fourth term isparticularly a problem because a frequency is high. This is referred tobelow.

The delay T is further added to a left side of Equation (125). FIG. 13shows such a transmission procedure. As shown in FIG. 13, an additionvalue of a detected phase in this case is the same irrespective of theaddition of the delay T. Therefore, the following Equation (126) isobtained:

θ_(H1)(t+T)+θ_(H2)(t+t ₀T)=θ_(τH1)+θ_(τH2)+{(ω_(B1)−ω_(B2))+(ω_(C1)−ω_(C2))}t ₀   (126)

A right side of Equation (126) described above and a right side ofEquation (125) described above are the same. That is, if a relative timedifference is the same (in the example explained above, T), an additionresult of a phase in which a signal transmitted from the device 1 isreceived by the device 2 and a phase in which a signal transmitted fromthe device 2 is received by the device 1 does not change irrespective ofthe delay T. That is, the addition result of the phases is a value thatdoes not depend on the delay T.

Transmission and reception of the angular frequency ω_(C1)−ω_(B1) signalbetween the device 1 and the device 2 is explained the same. That is,the following Equations (127) and (128) are obtained from Equations (47)and (57) described above:

θ_(L1)(t)+θ_(L2)(t+t₀)=θ_(τL1)+θ_(τL2)+{−(ω_(B1)−ω_(B2))+(ω_(C1)−ω_(C2))}t ₀   (127)

θ_(L1)(t+T)+θ_(L2)(t+t ₀T)=θ_(τL1)+θ_(τL2)+{−(ω_(B1)−ω_(B2))+(ω_(C1)−ω_(C2))}t ₀   (128)

From the above examination, a sequence is considered in which, aftertransmission and reception in both directions of the angular frequencyω_(C1)+ω_(B1) signal, transmission of reception of the angular frequencyω_(C1)−ω_(B1) signal is performed. When a transmission start time of theangular frequency ω_(C1)−ω_(B1) signal from the device 1 is representedas T on a basis of a transmission start time of the angular frequencyω_(C1)+ω_(B1) signal, the following Equation (129) is obtained fromEquations (125) and (128) describe above, where T>t₀ is assumed.

θ_(H1)(t)+θ_(H2)(t+t ₀)−{θ_(L1)(t+T)+θ_(L2)(t+t ₀+T)}=θ_(τH1)−θ_(τL1)+θ_(τH2)−θ_(τL2)+2(ω_(B1)−ω_(B2))t ₀   (129)

A last term of a left side of Equation (129) described above is a phaseerror due to a transmission delay. A delay error due to a received localfrequency for high-frequency is cancelled by calculating a differencebetween the angular frequency ω_(C1)+ω_(B1) signal and the angularfrequency ω_(C1)−ω_(B1) signal. Therefore, the phase error is, in termsof time series, multiplication of a shortest delay time t₀ and an errorof a local angular frequency (e.g., 2π×5 MHz) for a baseband processing.If the delay time t₀ is set small, the error is small. Therefore,depending on a value of the delay time t₀, practically, it is consideredpossible to perform distance measurement without a problem in accuracy.

A method of removing the last term of Equation (129) described above,which is a distance estimation error factor, is explained.

The following Equation (130) is obtained from Equations (27) and (37)described above:

θ_(H1)(t+t₀)+θ_(H2)(t)=θ_(τH1)+θ_(τH2)−{(ω_(B1)−ω_(B2))+(ω_(C1)−ω_(C2))}t ₀  (130)

Even if a predetermined delay D is added to a left side of Equation(130), as explained above, a value of a right side does not change.Therefore, the following Equation (131) is obtained:

θ_(H1)(t+t ₀+D)+θ_(H2)(t+D)=θ_(τH1)+θ_(τH2)−{(ω_(B1)−ω_(B2))+(ω_(C1)−ω_(C2))}t ₀  (131)

When the Equations (125) and (131) are added up, the following Equation(132) is obtained:

θ_(H1)(t)+θ_(H2)(t+t ₀)+θ_(H1)(t +t ₀ +D)+θ_(H2)(t+D)=2(74_(τH1)+θ_(τH2))   (132)

A left side of FIG. 14 shows a state of Equation (132) described above.When D=t₀ in Equation (132), the following Equation (133) is obtained:

θ_(H1)(t)+2θ_(H2)(t+t ₀)+θ_(H1)(t+2t ₀)=2(θ_(τH1)+θ_(τH2))   (133)

A right side of Equation (133) described above is only a term of a radiowave propagation delay corresponding to a distance that does not dependon time.

From Equations (47) and (57) described above, the following Equation(134) is obtained:

θ_(L1)(t+t₀)+θ_(L2)(t)=θ_(τL1)+θ_(τL2)−{−(ω_(B1)−ω_(B2))+(ω_(C1)−ω_(C2))}t ₀  (134)

Even if the predetermined delay D is added to a left side of Equation(134), a value of a right side does not change. Therefore, the followingEquation (135) is obtained:

θ_(L1)(t+t ₀D)+θ_(L2)(t+D)=θ_(τL1)+θ_(τL2)−{−(ω_(B1)−ω_(B2))+(ω_(C1)−ω_(C2))}t ₀  (135)

When Equations (127) and (135) described above are added up, thefollowing Equation (136) is obtained:

θ_(L1)(t)+θ_(L2)(t+t ₀)+θ_(L1)(t+t ₀ +D)+θ_(L2)(t+D)=2(θ_(τL1)+θ_(τL2))  (136)

In Equation (136), when D=t₀, the following Equation (137) is obtained:

θ_(L1)(t)+2θ_(L2)(t+t ₀)+θ_(L1)(t+2t ₀)=2(θ_(τL1)+θ_(τL2))   (137)

A right side of Equation (137) described above is only a term of a radiowave propagation delay corresponding to a distance that does not dependon time.

Equations (133) and (137) described above mean a sequence for performingphase detection of a transmission signal of the device 1 in the device2, performing phase detection of a transmission signal of the device 2in the device 1 after t₀, and performing the phase detection of thetransmission signal of the device 1 in the device 2 again after 2t₀. Inthe following explanation, the process in which transmission of thetransmission signal of the device 1 and phase detection in the device 2for the transmission signal and transmission of the transmission signalof the device 2 and phase detection in the device 1 for the transmissionsignal alternate and the phase detections are measured again by shiftingtime is referred to as “repeated alternation”.

That is, the repeated alternation for respectively transmitting andreceiving two carrier signals in the devices 1 and 2 and transmittingand receiving the carrier signal again at a to interval from the device1 or 2 to the other device is performed. Consequently, although theorder and time of the transmission are limited, it is possible toperform accurate distance measurement that does not depend on time.

Further, depending on a transmission and reception sequence of carriersignals, even if the repeated alternation is not performed at the tointerval, it is possible to perform accurate distance measurement thatdoes not depend on time.

That is, even if a fixed delay T is added to a left side of Equation(136) described above, a right side is fixed. Therefore, the followingEquation (138) is obtained:

θ_(L1)(t+T)+θ_(L2)(t+t ₀ +T)+θ_(L1)(t+t ₀+D+T)+θ_(L2)(t+D+T)=2(θτ_(L1)+θτ_(L2))   (138)

The following Equation (139) is obtained from Equations (132) and (138)described above:

θ_(H1)(t)+θ_(H2)(t+t ₀)+θ_(H1)(t+t ₀+D)+θ_(H2)(t+D)−{θ_(L1)(t+T)+θ_(L2)(t+t ₀ +T)+θ_(L1)(t+t ₀+D+T)+θ_(L2)(t+D+T)}=2{(θ_(τH1)−θ_(τL1))+(θ_(τH2)−θ_(τL2))}=4×(ω_(B1)+ω_(B2))τ₁  (139)

Equation (139) described above indicates a sequence for, afterperforming the repeated alternation of reciprocation of the angularfrequencies ω_(C1)+ω_(B2) signal and ω_(C2)+ω_(B2) signal at the timeinterval D, performing the repeated alternation of reciprocation of theangular frequencies ω_(C1)−ω_(B1) signal and ω_(C2)−ω_(B2) signal at thetime interval D after T from a measurement start. By adopting thissequence, it is possible to remove a distance estimation error factor ofthe last term of Equation (129) described above and perform accuratedistance measurement.

FIGS. 14 and 15 show the sequence. It is possible to extract only apropagation delay component by measuring a phase in such a sequence.That is, the control section 11 of the device 1 transmits a transmissionwave having the angular frequency ω_(C1)+ω_(B1) (hereinafter referred toas transmission wave H1A) at predetermined timing. Immediately afterreceiving the transmission wave H1A, the control section 21 of thedevice 2 transmits a transmission wave having the angular frequencyω_(C2)+ω_(B2) (hereinafter referred to as transmission wave H2A).Further, after transmitting the transmission wave H2A, the controlsection 21 of the device 2 transmits a transmission wave having theangular frequency ω_(C2)+ω_(B2) (hereinafter referred to as transmissionwave H2B). After receiving the second transmission wave H2B, the controlsection 11 of the device 1 transmits a transmission wave having theangular frequency ω_(C1)+ω_(B1) (hereinafter referred to as transmissionwave H1B).

Further, the control section 11 transmits a transmission wave having theangular frequency ω_(C1)−ω_(B1) (hereinafter referred to as transmissionwave L1A). Immediately after receiving the transmission wave L1A, thecontrol section 21 of the device 2 transmits a transmission wave havingthe angular frequency ω_(C2)−ω_(B2) (hereinafter referred to astransmission wave L2A). Further, after transmitting the transmissionwave L2A, the control section 21 of the device 2 transmits atransmission wave having the angular frequency ω_(C2)−ω_(B2)(hereinafter referred to as transmission wave L2B). After receiving thesecond transmission wave L2B, the control section 11 of the device 1transmits a transmission wave having the angular frequency ω_(C1)−ω_(B1)(hereinafter referred to as transmission wave L1B).

In this way, as shown in FIGS. 14 and 15, the control section 21 of thedevice 2 acquires a phase θ_(H1)(t) based on the transmission wave H1Ain a predetermined time from a predetermined reference time 0, acquiresa phase θ_(H1)(t+t₀+D) based on the transmission wave H1B in apredetermined time from a time t₀+D, acquires a phase θ_(L1)(t+T) basedon the transmission wave L1A in a predetermined time from the time T,and acquires a phase θ_(L1)(t+t₀+D+T) based on the transmission wave L1Bin a predetermined time from a time t₀+D+T.

The control section 11 of the device 1 acquires a phase θ_(H2)(t+t₀)based on the transmission wave H2A in a predetermined time from a timet₀, acquires a phase θ_(H2)(t+D) based on the transmission wave H2B in apredetermined time from a time D, acquires a phase θ_(L2)(t+t₀+T) basedon the transmission wave L2A in a predetermined time from a time t₀+T,and acquires a phase θ_(L2)(t+D+T) based on the transmission wave L2B ina predetermined time from a time D+T.

At least one of the devices 1 and 2 transmits phase information, thatis, calculated four phases or two phase differences or an operationresult of Equation (139) described above of the phase differences. Thecontrol section of the device 1 or 2, which receives the phaseinformation, calculates a distance according to an operation of Equation(139) described above. Note that, although “calculate a phasedifference” is described in steps S7 and S17 in FIG. 6, in this case, itis not always necessary to calculate a phase difference in steps S7 andS17. A phase difference may be calculated during the distancecalculation in S19.

In this way, in the present embodiment, by repeatedly alternating thecarrier signals from the first device and the second device, even whenthe carrier signals cannot be simultaneously transmitted and received,it is possible to perform accurate distance measurement. For example,the first device and the second device respectively transmit signalshaving two angular frequencies twice to the second device and the firstdevice in a predetermined sequence and calculate phase differencesrespectively in the first and second devices. Any one of the firstdevice and the second device transmits calculated phase information tothe other. The device, which receives the phase information, calculatesa distance between the first device and the second device on a basis ofeight phases calculated by the first device and the second device.Consequently, the distance between the first device and the seconddevice is accurately calculated irrespective of initial phases of theoscillators of the first device and the second device. In this way, evenwhen signals having respective angular frequencies are notsimultaneously transmitted and are transmitted and received at timingsshifted from each other, it is possible to remove an error of distanceestimation and perform accurate distance measurement.

(Problems of the Multipath)

In the above explanation, the device 2 receives the transmission signaltwo waves having the angular frequencies ω_(C1)+ω_(B1) and ω_(C1)−ω_(B2)from the device 1 and detects the phases θ_(H1)(t) and θ_(L1)(t). Thedevice 1 receives the transmission signal two waves having the angularfrequencies ω_(C2)+ω_(B2) and ω_(C2)−ω_(B2) from the device 2 anddetects the phases θ_(H2)(t) and θ_(L2)(t). It is possible to performthe distance measurement using these four phases.

However, there is a problem that a phase of a received wave changesbecause of an influence of the multipath and a phase of a propagationdelay corresponding to a distance cannot be accurately extracted. Thisproblem is explained below using a two-wave model put under strictconditions in the influence of the multipath.

FIG. 16 is an explanatory diagram for explaining the problem due to sucha multipath environment in the distance measurement.

As shown in FIG. 16, a sine wave y(t′)=sin ωt′ transmitted from anautomobile C reaches a key K via a route (a distance R) in which thesine wave y(t′)=sin ωt′ is directly propagated to the key K and anotherroute (a distance R+ΔR) in which the sine wave y(t′)=sin ωt′ isreflected on a wall W and propagated to the key K. A propagation delayof a direct wave passing through the route in which the sine wavey(t′)=sin ωt′ is directly propagated from the automobile C to the key Kis τ. A propagation delay of a delayed wave passing through the route inwhich the sine wave y(t′)=sin ωt′ is reflected on the wall W andpropagated from the automobile C to the key K is τ+τ₁.

It is assumed that the key K receives two waves, that is, a wavepropagated through a route in which the wave is propagated to the key Kat the propagation delay τ and a wave propagated through a route inwhich the wave is reflected on a wall and propagated to the key at apropagation delay τ+τ₁. In this case, a signal y(t′) received by the keyK is a signal obtained by adding up the two waves and is represented bythe following Equation (69):

y(t′)=sin{ω(t′−τ)}+A sin{ω(t′−τ−τ ₁)+θ₁}  (69)

In the equation, θ₁ represents a phase shift that occurs when the waveis reflected on the wall. A represents amplitude that is set taking intoaccount a loss due to the reflection and a propagation loss of adistance error ΔR. To simplify the calculation, t is set as t=t′−τ. Asignal at time tin the key K is represented by the following Equation(70):

y(t)=sin ωt+A sin{ω(t−τ ₁)+θ₁}={1+Acos(ωτ₁−θ₁)} sim ωt−A sin(ωτ−θ₁)cosωt   (70)

When Equation (70) described above is modified using a compositionformula of trigonometric functions, the following Equations (71) and(72) are obtained:

y(t)={1+A ²+2A cos(ωτ₁−θ₁)}^(1/2) sin(ωt+ϕ)   (71)

ϕ=−tan⁻¹(A sin(ωτ₁−θ₁)/{1+A cos(ωτ₁−θ₁)}  (72)

It is shown from Equations (71) and (72) that, because of an influenceof a delayed wave A sin{ω(t-π₁)+θ₁} reflected on the wall W, amplitudeand a phase of a received signal of the key K change compared with acase of only a direct wave. A phase change corresponding to an angularfrequency ω=ω_(C1)+ω_(B1) is represented as ϕ_(H) and a phase changecorresponding to an angular frequency ω=ω_(C1)−ω_(B1) is represented asϕ_(L). When a difference ϕ_(L)−ϕ_(H) of the phase changes is calculated,the following Equation (73) is obtained:

ϕ_(L)−ϕ_(H)=−tan⁻[A sin{(ω_(C1)−ω_(B1))τ₁−θ₁}]/[1Acos{(ω_(C1)−ω_(B1))τ₁−θ₁}]+tan⁻¹[A sin{(ω_(C1)+ω_(B1))τ₁−θ₁}]/[1+Acos{(ω_(C1)+ω_(B1))τ₁−θ₁}]  (73)

Equation (73) described above indicates a phase detection error causedby presence of the delayed wave. In the equation, τ₁ represents a delaytime of the delayed wave with respect to the direct wave and is a valueproportional to a difference of a propagation distance. As it is shownfrom Equation (73), ϕ_(L)−ϕ_(H) depends on θ₁. However, ϕ_(L)−ϕ_(H)depends on a reflecting object and an incident angle unrelated to thepropagation distance.

FIG. 17 is a graph showing a relation between the delay time τ₁ and thedifference ϕ_(L)−ϕ_(H) of a phase change with time plotted on thehorizontal axis and amplitude plotted on the vertical axis. Note that,in FIG. 17, a relation in a case of A=0.5, θ₁=0(rad), τ=16.8(ns),ω_(C1)=2π×900 M(Hz), and ω_(B1)=2π×5 M(Hz) is shown.

Since a difference of a delay time between the direct wave and thedelayed wave is τ₁, the phase changes ϕ_(H) and ϕ_(L), angularfrequencies of which respectively correspond to ω_(C1)+ω_(B1) andω_(C1)−ω_(B1), are represented by the following Equations (74) and (75):

ϕ_(H)=(ω_(C1)+ω_(B1))τ₁   (74)

ϕ_(L)=(ω_(C1)−ω_(B1))τ₁   (75)

From Equations (74) and (75), since τ₁=(ϕ_(H)−ϕ_(L))/2ω_(B1), thedistance error ΔR due to a difference of a path is represented by thefollowing Equation (76):

ΔR=cτ ₁ =c×(ϕ_(H)−ϕ_(L))/(2ω_(B1))   (76)

When ω_(B1)=2π×5 M(Hz), τ₁ is about 16 (ns), −0.80≤ϕ_(H)−ϕ_(L)≤0.4. Inthis case, the distance error ΔR is approximately 1.9 m to 3.8 m. Thatis means, when 2 m is requested as distance accuracy in the distancemeasuring system under such a condition, distance measurement isperformed with an unallowable distance error. Therefore, in this case,it is necessary to compensate for the influence due to the multipath.

(Specific Example for Solving the Problems)

Therefore, in the present embodiment, the transmitting sections 14 and24 transmit a signal having an angular frequency ω=ω_(C1) separatelyfrom the transmission waves having the angular frequenciesω=ω_(C1)+ω_(B1)and ω=ω_(C1)−ω_(B1).

A result obtained by calculating amplitude ratios of the three waves,specifically, an amplitude ratio ΔA_(H0) of the angular frequencyω_(C1)+ω_(B1) with respect to the angular frequency ω_(C1) and anamplitude ratio ΔA_(L0) of the angular frequency ω_(C1)−ω_(B1) withrespect to the angular frequency ω_(C1) is used. The added signal havingthe angular frequency ω_(C1) is an average angular frequency ofω_(C1)+ω_(B1)and ω_(C1)−ω_(B1). However, an effect of the added signalis not lost even if the angular frequency of the added signal slightlydeviates from the average.

In the key K, concerning a received signal received at the time t, whenamplitude A_(H) at the angular frequency ω_(C1)+ω_(B1), amplitude A₀ atthe angular frequency ω_(C1), and amplitude A_(L) at the angularfrequency ω_(C1)−ω_(B1) are respectively calculated from Equation (71)described above, the following Equations (77) to (79) are obtained:

A _(H)=[1+A ²+2A cos{(ω_(C1)+ω_(B1))τ₁−θ₁}]^(1/2)   (77)

A ₀={1+A ²+2A cos(ω_(C1)τ₁−θ₁)}^(1/2)   (78)

A _(L)=[1+A ²+2A cos{(ω_(C1)−ω_(B1))τ₁−θ₁}]^(1/2)   (79)

However, it is assumed that the phase shift θ₁ caused by the wall Wduring the reflection is the same value in an applied frequency range.From Equations (77) to (79) described above, the following Equations(80) and (81) in which amplitude ratios ΔA_(H0) and ΔA_(L0) areindicated in decibel are obtained:

ΔA _(H0)=10 log{1+A ²+2A cos{(ω_(C1)−ω_(B1))τ₁−θ₁}}−10 log{1+A ²+2Acos(ω_(C1)τ₁−θ₁)}  (80)

ΔA _(L0)=10 log{1+A ²+2A cos{(ω_(C1)−ω_(B1))τ₁−θ₁}}−10 log{1+A ²+2Acos(ω_(C1)τ₁−θ₁)}  (81)

FIG. 18 is a graph showing a relation between Equations (80) and (81)described above and Δsum=Δ_(H0)+ΔA_(L0) and τ₁ by using the same displayas FIG. 17. In FIG. 18, θ₁=0(rad). Note that a change in θ₁ isequivalent to a shift of the horizontal axis τ₁. Shapes of respectivecharacteristic curves in the graph do not change.

As it is shown from comparison of FIG. 17 and FIG. 18, the delay time τ₁that takes a maximal value of Δsum=ΔA_(H0)+A_(L0) and a maximal value ofϕ_(H)−ϕ_(L) is equal. Therefore, under the consideration of this point,in the present embodiment, the phase difference ϕ_(H)+ϕ_(L) is correctedusing Δsum=ΔA_(H0)+ΔA_(L0).

FIG. 19 is a graph for explaining τ₁ dependency of ϕ_(L)−ϕ_(H) and τ₁dependency of Δsum/4=(ΔA_(H0)+ΔA_(L0))/4 by using the same display asFIGS. 17 and 18.

As shown in FIG. 19, a characteristic curve of ϕ_(H)−ϕ_(L) and acharacteristic curve of Δsum/4=(ΔA_(H0)+ΔA_(L0))/4 show changes that arenot the same but similar. If (ΔA_(H0)+ΔA_(L0))/4 is subtracted from aphase detected using two waves by making use of this relation, it ispossible to greatly reduce a phase error due to the multipath. Note thataddition of amplitude ratios is multiplied with (1/4). However, iftarget τ₁ is changed, (1/4) is not always an optimum value. Thismultiplication value is a design parameter and may be changed whennecessary.

When the distance error ΔR is calculated with respect to a valueobtained by subtracting (ΔA_(H0)+ΔA_(L0))/4 from the phase error due tothe multipath, the following Equation (82) is obtained:

ΔR={ϕ _(L)−ϕ_(H)|in rad−(ΔA _(H0) +ΔA _(L0)|in dB)/4}×c/(2ω_(B1))   (82)

FIG. 20 is a graph showing the distance error ΔR without correction andthe distance error ΔR with correction using the same display as FIGS. 17to 19. Note that the vertical axis of FIG. 20 indicates the distanceerror ΔR (m). It is shown from Equation (82) described above that, in arange in which τ₁ is 0 (ns) to 20 (ns), the distance error ΔR can bereduced to 1.8 m or less by subtracting (ΔA_(H0)+ΔA_(L0))/4 from adetected phase. In a range in which τ₁ is 0 (ns) to 10 (ns), thedistance error ΔR can be reduced to 1.2 m. In this way, in the presentembodiment, it is possible to improve distance accuracy by making use ofinformation concerning the amplitude ratios obtained using the threewaves.

(Operation of Distance Measurement in Which Three Waves Corresponding tothe Multipath are Used)

An operation of the distance measuring system is explained withreference to the flowchart of FIG. 21 concerning a case in which threewaves are used. In FIG. 21, the same procedures as the procedures inFIG. 6 are denoted by the same signs and explanation of the proceduresis omitted. In FIG. 21, an operation of the device 1 is shown on a leftside and an operation of the device 2 is shown on a right side. In FIG.21, an arrow connecting steps of the devices 1 and 2 indicates thatcommunication is performed between the devices 1 and 2.

As example shown in FIG. 21 is different from the flow shown in FIG. 6in that procedures in steps S21 and S22 are added on the device 1 sideand procedures in steps S31 to S34 are added on the device 2 side. StepS21 is a procedure for generating a transmission signal (an additionalsignal) of one wave having the angular frequency ω_(C1), which is anadditional signal of a third wave, from the device 1. Step S22 is aprocedure for transmitting an additional transmission wave of one wavebased on the generated additional signal.

When receiving the additional transmission wave in step S31, the device2 acquires I and Q signals in step S32 and calculates a distance errorin step S33. In step S34, the device 2 subtracts the distance error fromthe distance calculated in step S19 and calculates a corrected distance.

Note that, in the flow shown in FIG. 21, as in the flow shown in FIG. 6,it is not always necessary to calculate a phase difference in steps S7and S17. A phase difference may be calculated during the distancecalculation in step S19.

Other action is the same as the action shown in FIG. 6.

Incidentally, the calculation of the distance error in step S33 is basedon Equation (82) described above. The amplitude ratio ΔA_(H0) and theamplitude ratio ΔA_(L0) are not affected by time as indicated byEquations (80) and (81) described above. Therefore, the additionalsignal may be transmitted at any time timing. For example, in theexample shown in FIG. 21, the additional signal is transmitted after thephase difference calculation. The additional signal may be transmittedimmediately after transmission of two transmission waves or may betransmitted before the transmission of the two transmission waves.

In the example shown in FIG. 21, the device 2 receives the additionalsignal transmitted by the device 1 and calculates the distance error.However, it is also possible that the device 2 transmits an additionalsignal having an angular frequency ω_(c2), the device 1 calculates adistance error using the received additional signal and received twotransmission waves and transmits information concerning the calculateddistance error to the device 2, and the device 2 corrects a distance.

Other action is the same as the action in the case in which the twowaves are used.

As explained above, in the present embodiment, by transmitting the twowaves of the carrier signals from the first device and the second deviceto each other and transmitting the one wave of the additional signal, itis possible to calculate a distance error in the multipath and performdistance measurement with the influence of the multipath reduced.

Note that the processing concerning the multipath, the calculationprocessing of a distance by the residue of 2π, the selection processingfrom the plurality of distance candidates, the processing in thetime-series transmission and reception, and the like can be used incombination as appropriate.

Second Embodiment

FIGS. 22 and 23 are explanatory diagrams showing a second embodiment ofthe present invention. The present embodiment indicates an example inwhich the respective distance measuring systems are applied to a smartentry system.

In FIG. 22, a key 31 can transmit, by radio, a signal for enablingunlocking and locking of a door of an automobile 32 and a start of anengine of the automobile 32. That is, the key 31 includes a not-showndata transmitting/receiving section and can transmit encrypted peculiardata for authentication with the data transmitting/receiving section. Aradio wave from the data transmitting/receiving section of the key 31 isreceived in a not-shown vehicle control device 35 mounted on theautomobile 32.

As shown in FIG. 23, a control section 36 is provided in the vehiclecontrol device 35. The control section 36 controls respective sectionsof the vehicle control device 35. The control section 36 is configuredof a processor including a CPU. The control section 36 may operate acomputer program stored in a memory 38 and control the respectivesections.

A data transmitting/receiving section 37 is provided in the vehiclecontrol device 35. The data transmitting/receiving section 37 canperform wireless communication with the data transmitting/receivingsection of the key 31 via an antenna 35 a. The datatransmitting/receiving section 37 receives the peculiar data transmittedfrom the key 31 and transmits predetermined response data to the key 31to perform authentication of the key 31 and the automobile 32.

The data transmitting/receiving section 37 can finely set electric fieldintensity. The authentication is not performed unless the key 31 islocated in a relatively close position where the key 31 is capable ofreceiving transmission data of the data transmitting/receiving section37, that is, near the automobile 32.

For example, as indicated by a broken line in FIG. 22, it is assumedthat the key 31 is located sufficiently close to the automobile 32. Inthis case, the data transmitting/receiving section 37 is capable ofcommunicating with the key 31. The data transmitting/receiving section37 authenticates the key 31 through collation with peculiar datarecorded in a memory 37 a. The data transmitting/receiving section 37outputs a signal indicating that the key 31 is authenticated to thecontrol section 36. Consequently, the control section 36 controls anunlocking/locking device 39 to give permission of locking or unlocking.

In FIG. 22, attackers of a relay attack carry relay devices 33 and 34.The relay device 33 is capable of communicating with the key 31. Therelay device 34 is capable of communicating with the datatransmitting/receiving section 37 in the automobile 32. The relaydevices 33 and 34 relay communication between the key 31 and the datatransmitting/receiving section 37. Consequently, even when the key 31 issufficiently separated from the automobile 32 as shown in FIG. 22 anddirect communication between the key 31 and the datatransmitting/receiving section 37 cannot be performed, the datatransmitting/receiving section 37 can authenticate the key 31 throughthe relay devices 33 and 34.

Therefore, in the present embodiment, the control section 36 determineson a basis of an authentication result of the datatransmitting/receiving section 37 and a distance measurement result fromthe second device 2 whether unlocking and locking, a start of theengine, and the like are permitted.

The second device 2 in the first embodiment is incorporated in the key31. On the other hand, the device 1 in the first embodiment is mountedon the vehicle control device 35. A transmission wave from the device 1is received in the device 2 via an antenna 27 a. A transmission wavefrom the device 2 is received in the device 1 via the antenna 27 a. Thetransmission wave from the device 1 is directly received by the antenna27 a in some cases and is received by the antenna 27 a through the relaydevices 33 and 34 in other cases. Similarly, the transmission wave fromthe second device 2 is directly received by the device 1 from theantenna 27 a in some cases and is received by the device 1 from theantenna 27 a through the relay devices 33 and 34.

When it is assumed that phases of the transmission waves from the device1 and the device 2 do not change in the relay devices 33 and 34, thedevice 2 can calculate a distance from the key 31 on a basis of thephases calculated in the devices 1 and 2. The device 2 outputs thecalculated distance to the control section 36. A distance threshold forpermitting authentication of the key 31 is stored in the memory 38. Whenthe distance calculated by the device 2 is within the distance thresholdread out from the memory 38, the control section 36 assumes that the key31 is authenticated and permits unlocking and locking, a start of theengine, and the like. When the distance calculated by the device 2 islarger than the distance threshold read out from the memory 38, thecontrol section 36 does not permit the authentication of the key 31.Therefore, in this case, the control section 36 does not permitunlocking and locking, a start of the engine, and the like.

Note that the relay devices 33 and 34 can change the phases of thetransmission waves from the device 1 and the device 2. Even in thiscase, since initial phases of the devices 1 and 2 are unknown, the relaydevices 33 and 34 cannot calculate a phase shift amount necessary forkeeping the distance calculated by the device 2 within the distancethreshold read out from the memory 38. Therefore, even if the relaydevices 33 and 34 are used, possibility that the authentication of thekey 31 is permitted is sufficiently small.

As explained above, in the present embodiment, by using the distancemeasuring system in the first embodiment, it is possible to preventunlocking and the like of a vehicle from being performed by a relayattack to the smart entry system.

(Transmission Sequence)

FIGS. 24 to 35 are explanatory diagrams showing various sequencesadoptable in the respective embodiments.

FIG. 24 shows a sequence in which the carrier sense is performed, aresponse is absent, and the repeated alternation is absent. This exampleof the sequence is an example in which presence or absence of a distancemeasurement frequency is determined by the carrier sense. When thedistance measurement frequency is sensed by the carrier sense, (a) thesequence may be started from the beginning again after a predeterminedtime (e.g., several milliseconds) or (b) may be started in the carriersense exception sequence. Note that the transmission wave having thecenter frequency is a transmission wave for calculating only amplituderatios with respect to other transmission waves and may be measured atany timing after or before reception of the respective transmissionwaves.

FIG. 25 shows a sequence in which the carrier sense is performed, aresponse is absent, and the repeated alternation is present. Thisexample of the sequence is also an example in which presence or absenceof a distance measurement frequency is determined by the carrier sense.When the distance measurement frequency is sensed by the carrier sense,(a) the sequence may be started from the beginning again after apredetermined time (e.g., several milliseconds) or (b) may be started inthe carrier sense exception sequence. Note that the transmission wavehaving the center frequency is a transmission wave for calculating onlyamplitude ratios with respect to other transmission waves and may bemeasured at any timing before or after reception of the respectivetransmission waves.

FIG. 26 shows a sequence in which the carrier sense is performed, aresponse is present, and the repeated alternation is present. Thisexample of the sequence is also an example in which presence or absenceof a distance measurement frequency is determined by the carrier sense.When the distance measurement frequency is sensed by the carrier sense,(a) the sequence may be started from the beginning again after apredetermined time (e.g., several milliseconds) or (b) may be started inthe carrier sense exception sequence. Note that the transmission wavehaving the center frequency is a transmission wave for calculating onlyamplitude ratios with respect to other transmission waves and may bemeasured at any timing before or after reception of the respectivetransmission waves.

FIG. 27 shows a sequence in which the carrier sense is absent, aresponse is absent, and the repeated alternation is absent. Note thatthe transmission wave having the center frequency is a transmission wavefor calculating only amplitude ratios with respect to other transmissionwaves and may be measured at any timing before or after reception of therespective transmission waves.

FIG. 28 shows a sequence in which the carrier sense is absent, aresponse is absent, and the repeated alternation is present. Note thatthe transmission wave having the center frequency is a transmission wavefor calculating only amplitude ratios with respect to other transmissionwaves and may be measured at any timing before or after reception of therespective transmission waves.

FIG. 29 shows a sequence in which the carrier sense is absent, aresponse is present, and the repeated alternation is present.

FIG. 30 shows a sequence in which the carrier sense is present in somecases and is absent in other cases, a response is absent, and therepeated alternation is absent. This example of the sequence is also anexample in which presence or absence of a distance measurement frequencyis determined by the carrier sense. When the distance measurementfrequency is sensed by the carrier sense, (a) the sequence may bestarted from the beginning again after a predetermined time (e.g.,several milliseconds) or (b) may be started in the carrier senseexception sequence. Note that the transmission wave having the centerfrequency is a transmission wave for calculating only amplitude ratioswith respect to other transmission waves and may be measured at anytiming before or after reception of the respective transmission waves.

FIG. 31 shows a sequence in which the carrier sense is present in somecases and is absent in other cases, a response is absent, and therepeated alternation is absent. This example of the sequence is also anexample in which presence or absence of a distance measurement frequencyis determined by the carrier sense. When the distance measurementfrequency is sensed by the carrier sense, (a) the sequence may bestarted from the beginning again after a predetermined time (e.g.,several milliseconds) or (b) may be started in the carrier senseexception sequence. Note that the transmission wave having the centerfrequency is a transmission wave for calculating only amplitude ratioswith respect to other transmission waves and may be measured at anytiming before or after reception of the respective transmission waves.

FIG. 32 shows a sequence in which the carrier sense is present in somecases and is absent in other cases, a response is absent, and therepeated alternation is present. This example of the sequence is also anexample in which presence or absence of a distance measurement frequencyis determined by the carrier sense. When the distance measurementfrequency is sensed by the carrier sense, (a) the sequence may bestarted from the beginning again after a predetermined time (e.g.,several milliseconds) or (b) may be started in the carrier senseexception sequence. Note that the transmission wave having the centerfrequency is a transmission wave for calculating only amplitude ratioswith respect to other transmission waves and may be measured at anytiming before or after reception of the respective transmission waves.

FIG. 33 shows a sequence in which the carrier sense is present in somecases and is absent in other cases, a response is present, and therepeated alternation is present. This example of the sequence is also anexample in which presence or absence of a distance measurement frequencyis determined by the carrier sense. When the distance measurementfrequency is sensed by the carrier sense, (a) the sequence may bestarted from the beginning again after a predetermined time (e.g.,several milliseconds) or (b) may be started in the carrier senseexception sequence. Note that the transmission wave having the centerfrequency is a transmission wave for calculating only amplitude ratioswith respect to other transmission waves and may be measured at anytiming before or after reception of the respective transmission waves.

FIG. 34 shows a sequence in which the carrier sense is performed, aresponse is present, and the repeated alternation is present. Thisexample of the sequence is also an example in which presence or absenceof a distance measurement frequency is determined by the carrier sense.When the distance measurement frequency is sensed by the carrier sense,(a) the sequence may be started from the beginning again after apredetermined time (e.g., several milliseconds) or (b) may be started inthe carrier sense exception sequence. Note that the transmission wavehaving the center frequency is a transmission wave for calculating onlyamplitude ratios with respect to other transmission waves and may bemeasured at any timing before or after reception of the respectivetransmission waves.

FIG. 35 shows a sequence in which the carrier sense is present in somecases and is absent in other cases, a response is present, and therepeated alternation is present. This example of the sequence is also anexample in which presence or absence of a distance measurement frequencyis determined by the carrier sense. When the distance measurementfrequency is sensed by the carrier sense, (a) the sequence may bestarted from the beginning again after a predetermined time (e.g.,several milliseconds) or (b) may be started in the carrier senseexception sequence. Note that the transmission wave having the centerfrequency is a transmission wave for calculating only amplitude ratioswith respect to other transmission waves and may be measured at anytiming before or after reception of the respective transmission waves.

(Modification Concerning the Multipath)

FIG. 36 is a flowchart for explaining an operation in a modification inwhich a multipath is taken into account and corresponds to FIG. 21. InFIG. 36, the same procedures as the procedures in FIG. 21 are denoted bythe same signs and explanation of the procedures is omitted.

As shown in FIG. 17, in the phase detection error (ϕ_(L)−ϕ_(H)) due tothe presence of the delayed wave, a maximal value occurs at apredetermined interval on a delay time difference axis. In other words,a value of the phase detection error ϕ_(L)−ϕ_(H) due to the presence ofthe delayed wave is small on the delay time difference axis on which amaximum value does not occur. As indicated by Equation (73) describedabove for obtaining the graph of FIG. 17, it is possible to reduce thevalue of the phase detection error ϕ_(L)−ϕ_(H) by changing the angularfrequencies ω_(C1) and ω_(B1). Note that, when a frequency difference isincreased or a frequency is set again to shift the center frequency,from Equations (80) and (81), the waveform shown in FIG. 18 is shiftedto the horizontal axis. Therefore, it is shown that it is possible toavoid a worst condition of phase deterioration.

Therefore, in the modification, it is determined whether phasefluctuation due to the delayed wave is large. When it is determined thatthe phase fluctuation is large, control for changing a carrier frequencyis performed. When it is determined that the phase fluctuation is small,a distance error is calculated to correct a distance.

For example, in the modification, it may be determined whether the phasefluctuation is large according to ΔA_(H0) and ΔA_(L0) calculated byEquations (80) and (81) described above. As it is evident from FIG. 18,both of ΔA_(H0) and ΔA_(L0) are positive when phase fluctuation due tothe path of the delay difference τ₁ is large. On the other hand, whenboth of ΔA_(H0) and ΔA_(L0) are negative, the phase fluctuation is alsolarge as it is evident from comparison of Equations (73) and (80).

Therefore, in the modification, the amplitude ratios ΔA_(H0) and ΔA_(L0)are observed. When both of ΔA_(H0) and ΔA_(L0) are positive or negative,it is determined that the phase error due to the multipath is relativelylarge. The frequency difference is increased, the center frequency isshifted, or a frequency is set again to perform distance measurement.Consequently, it is possible to reduce distance accuracy deterioration.

Note that, when an addition result of ΔA_(H0)+ΔA_(L0) is smaller than afirst predetermined threshold (TH1) or larger than a secondpredetermined threshold (TH2), it is also effective to determine thatthe phase error due to the multipath is large and perform the sameoperation.

FIG. 36 shows an example in which the second device calculates adistance. When acquiring I and Q signals in step S32, the controlsection 21 determines a distance error in the next step S41. Forexample, the control section 21 determines whetherTH1≤ΔA_(H0)+ΔA_(L0)≤TH2 holds. When TH1≤ΔA_(H0)+ΔA_(L0)≤TH2 holds, thecontrol section 21 determines that an error of a distance is relativelysmall, shifts the processing to step S33, and calculates a distanceerror.

On the other hand, when ΔA_(H0)+ΔA_(L0) is smaller than the thresholdTH1 or larger than the threshold TH2 in step S41, the control section 21determines that the phase error due to the multipath is large and shiftsthe processing to step S42. In step S42, the control section 21 sets acarrier frequency again and returns the processing to steps S3 and S13.When the same operation is repeated thereafter and it is determined thatthe distance error is relatively small, the distance is corrected.

Note that, in the flow shown in FIG. 36, as in the flow shown in FIG.21, a phase difference does not always need to be calculated in steps S7and S17. A phase difference may be calculated during the distancecalculation in step S19.

Note that, as indicated by Equation (82) described above, the correctionin step S34 in FIGS. 21 and 36 is correction for subtracting(ΔA_(H0)+ΔA_(L0)|in dB)/4 from the detected phase difference. However,to increase accuracy of the correction, it is also possible to performthe subtraction, for example, after intentionally distorting(ΔA_(H0)+ΔA_(L0)|in dB). An example is sin{(ΔA_(H0)+ΔA_(L0)|in dB)/4}.Although not shown in the figure, in this case, amplitude is compressedand phase accuracy is improved when the delay τ₁ is large according to asine function.

(Modification)

FIGS. 37 to 39 show a modification. In the modification, a period inwhich an initial phase should be fixed is explained. FIG. 37 is anexplanatory diagram showing a relation between a transmission sequenceand a period in which an initial phase is maintained. FIG. 38 is anexplanatory diagram showing a carrier frequency used for distancemeasurement. FIG. 39 is a flowchart for explaining the modification.

In the first embodiment, the simultaneous transmission and thesimultaneous reception of the respective two frequencies from thedevices 1 and 2 are assumed. In a period of the transmission andreception, the oscillators 13 and 23 are caused to continue oscillationsuch that the initial phase does not change. On the other hand, in thesecond embodiment, between the devices 1 and 2, it is specified thatonly one wave can be transmitted and received at the same time,transmission and reception of at least four waves necessary for distancemeasurement is carried out in time-series processing, and carriersignals from the devices 1 and 2 are repeatedly alternated to enableaccurate distance measurement even when the time-series transmission andreception is performed.

For example, as explained above, in the example shown in FIG. 15, thetransmission and reception of the transmission wave having the angularfrequency ω_(C1)+ω_(B1) from the device 1, the two times of transmissionand reception of the transmission wave having the angular frequencyω_(C2)+ω_(B2) from the device 2, and the transmission and reception ofthe transmission wave having the angular frequency ω_(C1)+ω_(B1) fromthe device 1 are performed.

Further, the transmission and reception of the transmission wave havingthe angular frequency ω_(C1)−ω_(B1) from the device 1, the two times oftransmission and reception of the transmission wave having the angularfrequency ω_(C2)−ω_(B2) from the device 2, and the transmission andreception of the transmission wave having the angular frequencyω_(C1)−ω_(B1) from the device 1 are performed.

An addition result of phases obtained in the devices 1 and 2 accordingto first transmission and reception of four waves in FIG. 15 is shown ina former half portion (first to fourth terms) of Equation (139)described above. The addition result of the first to fourth terms is2(θ_(τH1)+θ_(τH2)) as shown in Equation (132) described above. As shownin Equations (20) and (30) described above, the addition result does notinclude a term of an initial phase. That is, information concerning theinitial phase is not included in an operation result of phases obtainedby the first transmission and reception of the four waves in FIG. 15.Therefore, in an operation of the first to fourth terms of Equation(139) described above, a correct result is obtained if the initial phaseis not changed only in the transmission and reception period of the fourwaves.

Similarly, an addition result of phases obtained in the devices 1 and 2by last transmission and reception of fourth waves in FIG. 15 is shownin a latter half portion (fifth to eighth terms) of Equation (139)described above. The addition result of the fifth to eighth terms is2(θ_(τL1)+θ_(τL2)) as shown in Equation (138) described above. As shownin Equations (40) and (50) described above, the addition result does notinclude a term of an initial phase. That is, information concerning theinitial phase is not included in an operation result of phases obtainedby last transmission and reception of the four waves in FIG. 15.Therefore, in an operation of the fifth to eighth terms of Equation(139) described above, a correct result is obtained if the initial phaseis not changed only in the transmission and reception period of the fourwaves.

FIG. 37 shows this state and indicates that an initial phase ismaintained fixed in a distance measurement period in which the angularfrequencies ω_(C1)+ω_(B1) and ω_(C2)+ω_(B2) are used and an initialphase is maintained fixed in a distance measurement period in which theangular frequencies ω_(C1)−ω_(B1) and ω_(C2)−ω_(B2) are used.

That is, for example, when the sequence of FIG. 15 is adopted, it issufficient to cause the oscillators 13 and 23 to continue oscillationsuch that the initial phase does not change in a period of the firsttransmission and reception of the four waves and cause the oscillators13 and 23 to continue oscillation such that the initial phase does notchange in a period of last transmission and reception of the four waves.Even if the oscillation of the oscillators 13 and 23 stops and theinitial phase changes until transmission and reception of a fifth wavefrom transmission and reception of a fourth wave, an accurate distancecan be calculated on a basis of Equation (139) described above.

Incidentally, in the respective embodiments, the example is explained inwhich the two carrier signals transmitted by the devices 1 and 2 has afrequency of a sum of or a difference between, for example, therelatively high angular frequencies ω_(C1) and ω_(C2) and, for example,the relatively low angular frequencies ω_(B1) and ω_(B2). Note that theangular frequencies ω_(C1) and ω_(C2) are set to substantially the samefrequency and the angular frequencies ω_(B1) and ω_(B2) are set tosubstantially the same frequency.

(Concerning Two Carrier Signals)

However, in the distance measurement in the respective embodiments, asexplained below, the devices 1 and 2 only have to transmit two carriersignals respectively having predetermined frequency differences.

An angular frequency ω_(C)+ω_(B) and an angular frequency ω_(C)−ω_(B)can be modified as described below.

ω_(C)+ω_(B)=(ω_(C)−Δω_(C))+(Δω_(C)+ω_(B))=ω′_(C)+ω_(H)   (201)

ω_(C)−ω_(B)=(ω_(C)−Δω_(C))+(Δω_(C)−ω_(B))=ω′_(C)+ω_(L)   (202)

When transmission waves having the angular frequency we and the angularfrequency ω_(B) are represented as f_(C) and f_(B) on a frequency axis,transmission waves having the angular frequency ω_(C)+ω_(B) and theangular frequency ω_(C)−ω_(B) are as shown on a left side of FIG. 38.

Equations (201) and (202) described above indicate that a representationmethod is changed without changing a frequency. The transmission wavehaving the angular frequency ω_(C)+ω_(B) is obtained by a sum oftransmission waves having an angular frequency ω′_(C) and an angularfrequency ω_(H). The transmission wave having the angular frequencyω_(C)−ω_(B) is obtained by a sum of transmission waves having theangular frequency ω′_(C) and an angular frequency ω_(L).

The center in FIG. 38 shows transmission waves based on thisrepresentation. The transmission waves having the angular frequenciesω′_(C), ω_(H), and ω_(L) are respectively represented as f′_(C), f_(H),and f_(L) on the frequency axis. A transmission wave having a frequencyf_(C)−f_(B) and a transmission wave having a frequency f_(C)+f_(B) onthe left side of FIG. 38 respective indicates that the transmissionwaves can be represented as a transmission wave having the samefrequency f_(C)+f_(L) and a transmission wave having the same frequencyf′_(C)+f_(H).

That is, Equations (201) and (202) described above indicate that twocarriers transmitted by the devices 1 and 2 do not need to be obtainedby a sun of and a difference between two frequencies and the devices 1and 2 only have to generate two carriers having a predeterminedfrequency difference and transmit the carriers.

As an example in which the transmission waves having the angularfrequency ω_(C)+ω_(B) and the angular frequency ω_(C)−ω_(B) shown on theleft side of FIG. 38 are obtained, for example, the oscillators 13 and23 shown in FIG. 1 only have to generate a local signal having theangular frequency ω_(C) as a relatively high local frequency(hereinafter referred to as RF-LO frequency) and a local signal havingthe angular frequency ω_(B) as a relatively low local frequency(hereinafter referred to as IF-LO frequency) and the transmittingsection 14 and 24 only have to generate signals having a sum of or adifference between the local frequencies as transmission signals.

On the other hand, the transmission waves in the center of FIG. 38 areobtained by generating a local signal having the angular frequencyω′_(C) as the RF-LO frequency and generating two local signals havingthe angular frequencies ω_(L) and ω_(H) as the IF-LO frequency andgenerating, in the transmitting sections 14 and 24, signals having a sumof these local frequencies as transmission signals. That is, thetransmission waves in the center of FIG. 38 are obtained by fixing theRF-LO frequency and changing the IF-LO frequency.

The angular frequency ω_(C)−ω_(B) can be modified as shown below.

ω_(C)−ω_(B)=(ω_(C)−2ω_(B))+(2ω_(B)−ω_(B))=ω″_(C)−ω_(B)   (203)

A right side of FIG. 38 shows transmission waves based on therepresentation of Equation (203) and indicates that, when a transmissionwave having an angular frequency of ω″_(C) is represented as f″_(C) onthe frequency axis, the transmission wave having the frequencyf_(C)−f_(B) on the left side of FIG. 38 can be represented as atransmission wave having the same frequency f″_(C)+f_(B).

For example, the transmission waves on the right side of FIG. 38 areobtained by generating a local signal having the angular frequencyω′_(C) and a local signal having the angular frequencies ω″_(C) as theRF-LO frequency and generating a local signal having the angularfrequency ω_(B) as the IF-LO frequency and generating, in thetransmitting sections 14 and 24, signals having a sum of these localfrequencies as transmission signals. That is, the transmission waves onthe right side of FIG. 38 are obtained by fixing the IF-LO frequency andchanging the RF-LO frequency.

(Change of the Carrier Frequencies)

In this way, the devices 1 and 2 only have to transmit the two carriersignals respectively having the predetermined frequency difference inthe distance measurement. Moreover, when transmission and reception of acarrier having a higher frequency of the two carriers is alternatelyperformed and transmission and reception of a carrier having a lowfrequency is subsequently alternately performed as in the sequence shownin FIG. 15, initial phases may be different in the transmission andreception of the carrier having the high frequency and the transmissionand reception of the carrier having the low frequency.

Further, only the carrier having the high frequency is used for anoperation of Equation (132) described above obtained by decomposingEquation (139) described above and only the carrier having the lowfrequency is used for an operation of Equation (138) described above.That is, the operation of Equation (132) described above and theoperation of Equation (138) described above only have to beindependently performed. The local frequencies may be changed between atransmission and reception period of the carrier having the highfrequency and a transmission and reception period of the carrier havingthe low frequency.

When the change in the initial phase and the change in the carrierangular frequency are allowed, a flow shown in FIG. 39 can be adoptedinstead of the flow shown in FIG. 11A.

In the flow shown in FIG. 39, the device 1 sets a first local (LO)frequency before one wave transmission signal generation and the device2 sets a first local (LO) frequency before reception of one wavetransmission wave from the device 1. The device 1 generates a carrierhaving a high frequency, for example, as one wave transmission signalusing the local signal having the first LO frequency. The device 2receives the one wave transmission wave using the carrier having thehigh frequency and acquires I and Q signals.

After acquisition of the I and Q signals based on the transmissionsignal having the high frequency from the device 2 and before generationof the next one wave transmission signal, the device 1 sets a secondlocal (LO) frequency. Similarly, after the transmission of the one wavetransmission wave to the device 1 and before reception of the next onewave transmission wave, the device 2 sets a second local (LO) frequency.The device 1 generates a carrier having a low frequency, for example, asone wave transmission signal using the local signal having the second LOfrequency. The device 2 receives the transmission wave of the device 1using the carrier having the low frequency and acquires I and Q signals.

(Configuration Example of the Oscillators and the Transceivers)

In this way, the devices 1 and 2 only have to be capable of generatingand transmitting the two carrier signals having the predeterminedfrequency difference. Circuits having various configurations can beadopted as the oscillators 13 and 23, the transmitting sections 14 and24, and the receiving sections 15 and 25 in FIG. 1.

FIG. 40A is an explanatory diagram showing, in a simplified manner, anexample of the configurations of the oscillator 13, the transmittingsection 14, and the receiving section 15 of the device 1. FIG. 40B is anexplanatory diagram showing, in a simplified manner, an example of theconfigurations of the oscillator 23, the transmitting section 24, andthe receiving section 25 of the device 2.

As shown in FIGS. 40A and 40B, the device 1 and the device 2 include anoscillator that generates an IF-LO frequency and an oscillator thatgenerates an RF-LO frequency. Oscillation frequencies of the oscillatorsare, for example, fixed. Two carrier signals having a frequencydifference can be generated by adding the IF-LO frequency to orsubtracting the IF-LO frequency from the RF-LO frequency.

FIG. 41A is an explanatory diagram showing, in a simplified manner, anexample of the configurations of the oscillator 13, the transmittingsection 14, and the receiving section 15 of the device 1. FIG. 41B is anexplanatory diagram showing, in a simplified manner, an example of theconfigurations of the oscillator 23, the transmitting section 24, andthe receiving section 25 of the device 2.

The examples shown in FIGS. 41A and 41B are examples in which twocarrier signals having a frequency difference are generated by anoscillator having a variable frequency and a frequency divider (N-div).

FIG. 42 is a circuit diagram more specifically showing an example of acircuit that generates signals given to the multipliers TM11 and TM12 inFIG. 4. FIG. 43 is a circuit diagram more specifically showing anexample of a circuit that generates signals given to the multipliersTM21 and TM22 in FIG. 5.

In FIG. 42, a multiplier TM15 gives, to an adder TS15, a multiplicationresult of an I_(T) signal and a local signal cos(ω_(B1)t+θ_(B1)) fromthe oscillator 13. A multiplier TM16 gives, to the adder TS15, amultiplication result of a Q_(T) signal and a local signal±sin(ω_(B1)t+θ_(B1)) from the oscillator 13. The adder TS15 adds up thetwo inputs and gives an addition result to the multiplier TM11.

A multiplier TM17 gives, to an adder TS16, a multiplication result ofthe I_(T) signal and the local signal ±sin(ω_(B1)t+θ_(B1)) from theoscillator 13. A multiplier TM18 gives, to the adder TS16, amultiplication result of the Q_(T) signal and the local signalcos(ω_(B1)t+θ_(B1)) from the oscillator 13. The adder TS16 subtracts theoutput of a multiplier TM18 from the output of the multiplier TM17 andgives a subtraction result to the multiplier TM12. The other componentsare the same as the components shown in FIG. 4.

In FIG. 43, a multiplier TM25 gives, to an adder TS25, a multiplicationresult of the I_(T) signal and a local signal cos(ω_(B2)t+θ_(B2)) fromthe oscillator 23. A multiplier TM26 gives, to the adder TS25, amultiplication result of the Q_(T) signal and a local signal±sin(ω_(B2)t+θ_(B2)) from the oscillator 23. The adder TS25 adds up thetwo inputs and gives an addition result to the multiplier TM21.

A multiplier TM27 gives, to an adder TS26, a multiplication result ofthe I_(T) signal and the local signal ±sin(ω_(B2)t+θ_(B2)) from theoscillator 23. A multiplier TM28 gives, to the adder TS26, amultiplication result of the Q_(T) signal and the local signalcos(ω_(B2)t+θ_(B2)) from the oscillator 23. The adder TS26 subtracts theoutput of the multiplier TM28 from the output of the multiplier TM27 andgives a subtraction result to the multiplier TM22. The other componentsare the same as the components shown in FIG. 5.

FIG. 44 is a circuit diagram showing an example of specificconfigurations of the transmitting section 14 and the receiving section15 shown in FIG. 1. FIG. 45 is a circuit diagram showing an example ofspecific configurations of the transmitting section 24 and the receivingsection 25 shown in FIG. 1. Note that FIGS. 44 and 45 show transceivershaving a heterodyne configuration.

In FIG. 44, a multiplier TM1A gives, to an adder TS1A, a multiplicationresult of the I_(T) signal and the local signal cos(ω_(B1)t+θ_(B1)) fromthe oscillator 13. A multiplier TM1B gives, to the adder TS1A, amultiplication result of the Q_(T) signal and the local signalsin(ω_(B1)t+θ_(B1)) from the oscillator 13. The adder TS1A subtracts theoutput of the multiplier TM1B from the output of the multiplier TM1A andgives a subtraction result to a multiplier TM1C. The multiplier TM1Cmultiplies together the output of the adder TS1A and a local signalcos(ω_(C1)t+θ_(C1)) and outputs a multiplication result as thetransmission signal tx1.

A multiplier RM1A multiplies together the received signal rx1 and thelocal signal cos(ω_(C)t+θ_(C)) to obtain an I₁ signal and outputs the I₁signal to multipliers RM1B and RM1C. The multiplier RM1B outputs amultiplication result of the I₁ signal and the local signalcos(ω_(B1)t+θ_(B1)) as an I signal. The multiplier RM1C outputs amultiplication result of the I₁ signal and the local signalsin(ω_(B1)t+θ_(B1)) as a Q signal.

In FIG. 45, a multiplier TM2A gives, to an adder TS2A, a multiplicationresult of the I_(T) signal and the local signal cos(ω_(B2)t+θ_(B2)) fromthe oscillator 23. A multiplier TM2B gives, to the adder TS2A, amultiplication result of the Q_(T) signal and the local signalsin(ω_(B2)t+θ_(B2)) from the oscillator 23. The adder TS2A subtracts theoutput of the multiplier TM2B from the output of the multiplier TM2A andgives a subtraction result to a multiplier TM2C. The multiplier TM2Cmultiplies together the output of the adder TS2A and a local signalcos(ω_(C2)t+θ_(C2)) and outputs a multiplication result as thetransmission signal tx2.

A multiplier RM2A multiplies together the received signal rx2 and thelocal signal cos(ω_(C2)+θ_(C2)) to obtain the I₁ signal and outputs theI₁ signal to multipliers RM2B and RM2C. The multiplier RM2B outputs amultiplication result of the I₁ signal and the local signalcos(ω_(B2)t+θ_(B2)) as the I signal. The multiplier RM2C outputs amultiplication result of the I₁ signal and the local signalsin(ω_(B2)t+θ_(B2)) as the Q signal.

FIG. 46 is a circuit diagram showing an example of the specificconfigurations of the transmitting section 14 and the receiving section15 shown in FIG. 1. FIG. 47 is a circuit diagram showing an example ofthe specific configurations of the transmitting section 24 and thereceiving section 25 shown in FIG. 1. Note that FIGS. 46 and 47 showtransceivers in which a direct conversion scheme is adopted.

In FIG. 46, a multiplier TM1D gives, to an adder TS1C, a multiplicationresult of the I_(T) signal and the local signal cos(ω_(C1)t+θ_(C1)) fromthe oscillator 13. A multiplier TM1E gives, to the adder TS1C, amultiplication result of the Q_(T) signal and the local signalsin(ω_(C1)t+θ_(C1)) from the oscillator 13. The adder TS1C subtracts theoutput of the multiplier TM1E from the output of the multiplier TM1D andoutputs a subtraction result as the transmission signal tx1.

A multiplier RM1D multiplies together the received signal rx1 and thelocal signal cos(ω_(C1)t+θ_(C1)) and outputs a multiplication result asthe I signal. A multiplier RM1E multiplies together the received signalrx1 and the local signal sin(ω_(C1)t+θ_(C1)) and outputs amultiplication result as the Q signal.

In FIG. 47, a multiplier TM2D gives, to the adder TS2C, a multiplicationresult of the I_(T) signal and the local signal cos(ω_(C2)t+θ_(C2)) fromthe oscillator 23. A multiplier TM2E gives, to the adder TS2C, amultiplication result of the Q_(T) signal and the local signalsin(ω_(C2)t+θ_(C2)) from the oscillator 23. The adder TS2C subtracts theoutput of the multiplier TM2E from the output of the multiplier TM2D andoutputs a subtraction result as the transmission signal tx2.

A multiplier RM2D multiplies together the received signal rx2 and thelocal signal cos(ω_(C2)t+θ_(C2)) and outputs a multiplication result asthe I signal. A multiplier RM2E multiplies together the received signalrx2 and the local signal sin(ω_(C2)t+θ_(C2)) and outputs amultiplication result as the Q signal.

(Transmission Example of Phase Information)

In the respective embodiments, the phase information is transmitted fromeither one of the first device and the second device to the other.However, as explained above, a method of transmitting the phaseinformation is not particularly limited. For example, the phaseinformation may be transmitted by shifting by a phase obtained from areceived signal, a phase of a carrier signal to be transmitted.

For example, in this case, it is possible to adopt a flow in which thebroken line portion of FIG. 6 is replaced with a flow shown in FIG. 48and steps S7, S8, and S18 in FIG. 6 are omitted.

FIG. 48 is a flowchart for explaining an example corresponding to FIG.11A in which the second device transmits phase information to the firstdevice. FIG. 48 includes a step of adding up a received phase and aninitial phase between the acquisition step for the I and Q signals andthe one wave transmission signal generating step in the second deviceshown in FIG. 11A. Consequently, a carrier signal in which a phasedetected from a received signal is added to the initial phase of thedevice 2 is generated. The device 1 can acquire phase informationcalculated by the device 2 by receiving the carrier signal from thedevice 2 and calculating a phase.

FIG. 49 is a flowchart for explaining an example corresponding to FIG.39. A flow shown in FIG. 49 includes a step of adding up a receivedphase and an initial phase between the acquisition step for I and Qsignals and the one wave transmission signal generating step in thedevice 2 shown in FIG. 39 In this way, even when the carrier frequencyis changed halfway in the distance measurement, the phase informationmay be transmitted while being included in the information concerningthe phase of the carrier signal transmitted for the distancemeasurement.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel devices and methods describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modification as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A distance measuring device that calculates adistance on a basis of carrier phase detection, the distance measuringdevice comprising a calculating section configured to calculate, on abasis of phase information acquired by a first device and a seconddevice, at least one of which is movable, a distance between the firstdevice and the second device, wherein the first device includes a firstreference signal source, and a first transceiver configured to transmitthree or more first carrier signals having frequencies different fromone another and receive three or more second carrier signalsrespectively having frequencies substantially same as the frequencies ofthe three or more first carrier signals using an output of the firstreference signal source, the second device includes a second referencesignal source configured to operate independently from the firstreference signal source, and a second transceiver configured to transmitthe three or more second carrier signals and receive the three or morefirst carrier signals using an output of the second reference signalsource, the calculating section calculates the distance by a phasecalculation using a phase detection result obtained by reception of thefirst and second carrier signals having a substantially same frequencyand corrects the calculated distance on a basis of at least oneinformation of information concerning an amplitude ratio of the firstcarrier signals received by the second transceiver and informationconcerning an amplitude ratio of the second carrier signals received bythe first transceiver, and the calculating section acquires the phaseinformation and the information concerning the amplitude ratio after thefirst transceiver transmits a first wave and a second wave of the firstcarrier signals, the second transceiver transmits a first wave and asecond wave of the second carrier signals, the first transceiverreceives a first wave and a second wave of the second carrier signals,and the second transceiver receives a first wave and a second wave ofthe first carrier signals, and the first transceiver transmits a thirdwave of the first carrier signals, the second transceiver receives athird wave of the first carrier signals, and at least one of the secondtransceiver transmitting a third wave of the second carrier signals orthe first transceiver receiving the third wave of the second carriersignals.
 2. The distance measuring device according to claim 1, whereinthe calculating section acquires the phase information on a basis of thefirst wave and the second wave of the first carrier signals and thefirst wave and the second wave of the second carrier signals, and thecalculating section calculates at least one of a group includingamplitude ratios of the first wave and the third wave of the firstcarrier signals, and amplitude ratios of the second wave and the thirdwave of the first carrier signals, of a group including amplitude ratiosof the first wave and the third wave of the second carrier signals, andamplitude ratios of the second wave and the third wave of the secondcarrier signals.
 3. The distance measuring device according to claim 1,wherein the first transceiver transmits the first wave of the firstcarrier signal using the output of the first reference signal source,the second transceiver receives the first wave transmitted from thefirst transceiver and thereafter transmits the first wave of the secondcarrier signal and subsequently transmits the first wave of the secondcarrier signal again using the output of the second reference signalsource, the first transceiver receives, twice, the first wavetransmitted from the second transceiver and thereafter transmits thefirst wave of the first carrier signal again and subsequently transmitsthe second wave of the first carrier signal using the output of thefirst reference signal source, the second transceiver receives, inorder, the first wave and the second wave transmitted from the firsttransceiver and thereafter transmits the second wave of the secondcarrier signal and subsequently transmits the second wave of the secondcarrier signal again using the output of the second reference signalsource, the first transceiver receives, twice, the second wavetransmitted from the second transceiver and thereafter transmits thesecond wave of the first carrier signal again using the output of thefirst reference signal source, the first and second transceivers areconfigured such that, the second transceiver receives the second wavetransmitted from the first transceiver in a second time and thereaftertransmits the third wave of the second carrier signal using the outputof the second reference signal source, and the first transceiverreceives the third wave transmitted from the second transceiver usingthe output of the first reference signal source, or the firsttransceiver receives the second wave transmitted from the secondtransceiver in a second time using the output of the first referencesignal source and thereafter transmits the third wave of the secondcarrier signal, and the second transceiver receives the third wavetransmitted from the first transceiver.
 4. The distance measuring deviceaccording to claim 1, wherein the first transceiver transmits the firstwave of the first carrier signal using the output of the first referencesignal source after carrier sense of the first wave of the first carriersignal, the second transceiver receives the first wave transmitted fromthe first transceiver and thereafter transmits a first wave of thesecond carrier signal and subsequently transmits the first wave of thesecond carrier signal again after carrier sense of the first wave of thesecond carrier signal using the output of the second reference signalsource, the first transceiver receives, twice, the first wavetransmitted from the second transceiver and thereafter transmits thefirst wave of the first carrier signal again and subsequently transmitsa second wave of the first carrier signal after carrier sense of thesecond wave of the first carrier signal using the output of the firstreference signal source, the second transceiver receives, in order, thefirst wave and the second wave transmitted from the first transceiverand thereafter transmits a second wave of the second carrier signal andsubsequently transmits the second wave of the second carrier signalagain after carrier sense of the second wave of the second carriersignal using the output of the second reference signal source, the firsttransceiver receives, twice, the second wave transmitted from the secondtransceiver and thereafter transmits the second wave of the firstcarrier signal again using the output of the first reference signalsource, the first and second transceivers are configured such that, thesecond transceiver receives the second wave transmitted from the firsttransceiver in a second time and thereafter transmits a third wave ofthe second carrier signal after carrier sense of the third wave of thesecond carrier signal using the output of the second reference signalsource, and the first transceiver receives the third wave transmittedfrom the second transceiver using the output of the first referencesignal source, or the first transceiver receives the third wavetransmitted from the second transceiver using the output of the firstreference signal source and thereafter transmits a third wave of thesecond carrier signal, and the second transceiver receives the thirdwave transmitted from the first transceiver.
 5. A distance measuringdevice that calculates a distance between a first device and a seconddevice, at least one of which is movable, on a basis of phases of firstto sixth known signals transmitted with a plurality of carrierfrequencies, the distance measuring device comprising: the first deviceincluding a first reference signal source, and a first transceiverconfigured to transmit the first known signal corresponding to a firstcarrier frequency, the second known signal corresponding to a secondcarrier frequency different from the first carrier frequency, and thethird known signal corresponding to a third carrier frequency differentfrom the first and second carrier frequencies, and to receive the fourthknown signal corresponding to the first carrier frequency, the fifthknown signal corresponding to the second carrier frequency, and thesixth known signal corresponding to the third carrier frequency, usingan output of the first reference signal source; the second deviceincluding a second reference signal source configured to operateindependently from the first reference signal source, and a secondtransceiver configured to transmit the fourth known signal correspondingto the first carrier frequency, the fifth known signal corresponding tothe second carrier frequency, and the sixth known signal correspondingto the third carrier frequency, and to receive the first to third knownsignals, using an output of the second reference signal source; a firstphase detector provided in the first or second device, the first phasedetector being configured to detect phases of the fourth and fifth knownsignals received by the first transceiver; a second detector provided inthe first or second device, the second detector being configured todetect phases of the first and second known signals received by thesecond transceiver; and a calculating section provided in the first orsecond device, the calculating section being configured to calculate thedistance between the first device and the second device, wherein thecalculating section calculates the distance by correcting initial phasesof the first, second, fourth, and fifth known signals, a frequencydifference between the first and fourth known signals, and a frequencydifference between the second and fifth known signals, with the firsttransceiver and the second transceiver transmitting and receiving atleast one of the first, second, fourth, or fifth known signals by aplurality of times, and the calculating section corrects the calculateddistance on a basis of an amplitude ratio of the first, second, andthird known signals, or of the fourth, fifth, and sixth known signals,by a single time of transmission and reception of at least one of thethird or sixth known signals.
 6. A distance measuring device thatcalculates a distance between a first device and a second device, atleast one of which is movable, on a basis of phases of first to sixthknown signals transmitted with a plurality of carrier frequencies, thedistance measuring device comprising: the first device including a firstreference signal source. and a first transceiver configured to transmitthe first known signal corresponding to a first carrier frequency, thesecond known signal corresponding to a second carrier frequencydifferent from the first carrier frequency, and the third known signalcorresponding to a third carrier frequency different from the first andsecond carrier frequencies, and to receive the fourth known signalcorresponding to the first carrier frequency, the fifth known signalcorresponding to the second carrier frequency, and the sixth knownsignal corresponding to the third carrier frequency, using an output ofthe first reference signal source; the second device including a secondreference signal source configured to operate independently from thefirst reference signal source, and a second transceiver configured totransmit the fourth known signal corresponding to the first carrierfrequency, the fifth known signal corresponding to the second carrierfrequency, and the sixth known signal corresponding to the third carrierfrequency, and to receive the first to third known signals, using anoutput of the second reference signal source; a first phase detectorprovided in the first or second device, the first phase detector beingconfigured to detect phases of the fourth and fifth known signalsreceived by the first transceiver; a second detector provided in thefirst or second device, the second detector being configured to detectphases of the first and second known signals received by the secondtransceiver; and a calculating section provided in the first or seconddevice, the calculating section being configured to calculate thedistance between the first device and the second device, wherein thefirst transceiver and the second transceiver perform a total of seventimes of transmissions and receptions including six times oftransmissions and receptions including a plurality of times oftransmissions and receptions of at least one of the first, second,fourth, or fifth known signals, and a single time of transmission andreception of at least one of the third or sixth known signals, at leastone of the first phase detector or the second phase detector detects aphase with respect to the first, second, fourth, and fifth knownsignals, the calculating section calculates the distance between thefirst device and the second device by offsetting a frequency differencebetween the first known signal and fourth known signal and a frequencydifference between the second known signal and the fifth known signal byan operation including a difference operation of the phases, and thecalculating section corrects the calculated distance on a basis of anamplitude ratio with respect to the third known signal or the sixthknown signal.
 7. A distance measuring method that calculates a distancebetween a first device and a second device, at least one of which ismovable, on a basis of phases of first to sixth known signalstransmitted with a plurality of carrier frequencies, the distancemeasuring method comprising: transmitting, by a first device, the firstknown signal corresponding to a first carrier frequency, the secondknown signal corresponding to a second carrier frequency different fromthe first carrier frequency, and a third known signal corresponding to athird carrier frequency different from the first and second carrierfrequencies, and receiving the fourth known signal corresponding to thefirst carrier frequency, the fifth known signal corresponding to thesecond carrier frequency, and the sixth known signal corresponding tothe third carrier frequency, using an output of the first referencesignal source; transmitting, by the second device, the fourth knownsignal corresponding to the first carrier frequency, the fifth knownsignal corresponding to the second carrier frequency, and the sixthknown signal corresponding to the third carrier frequency, and receivingthe first to third known signals, using an output of a second referencesignal source configured to operate independently from the firstreference signal source; transmitting and receiving, by the first andsecond devices, at least one of the first, second, fourth, or fifthknown signals by a plurality of times, and transmitting and receiving atleast one of the third or sixth known signals once; and correcting, bythe calculating section, initial phases of the first, second, fourth,and fifth known signals, a frequency difference between the first andfourth known signals, and a frequency difference between the second andfifth known signals, to calculate the distance, on a basis of results ofa plurality of times of transmissions and receptions of at least one ofthe first, second, fourth, or fifth known signals, and calculating anamplitude ratio of the first, second, and third known signals, or of thefourth, fifth, and sixth known signals on a basis of a result of theonce transmission and reception of the at least one of the third orsixth known signals, to correct the calculated distance using thecalculated amplitude ratio.